it probably could do with a service as it is noisy, and sometimes misfeeds.
It looks like a well used gun so a service is probably a good thing.
Noise tells you a lot about what's happening inside a gun. Crunching/popping is generally bad but gear noise isn't so much a problem at 350fps.
The selector plate looks like it's a little worn, but functional. If it works leave it alone is the general rule of thumb. So I wouldn't replace that part. Just keep the biro spring nice and safe as it's a vital part.
Misfeeds are generally caused by a worn tappet plate. The tappet plate is an odd long bit of plastic that sits under the cylinder and holds the air nozzle in place. The place where they wear is at the lug where they get pulled back by the sector gear. Once they start to wear the air nozzle stops retracting fully. This stops the BB's getting up into the hop unit. A new tappet plate isn't expensive, but it must be matched to the gearbox type. In your case it's going to be a standard version 2.
https://www.ak2m4.co.uk/internal-parts/tappet-plates/zci-tappet-plate-v2
Grease is good. Just because it's thick and sticky doesn't mean it's not doing its job. The grease in the pistol grip looks to be silicone grease. It's a cheap grease that is suited to plastics, and metal on plastic applications.
Gear grease (metal on metal) comes in more variants than plastic greases. You want something that has the potential to lubricate, absorb sound, and stay moist. I use a soft moly grease. But there are loads of greases that will work.
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For rebuilding and servicing:
You need,
Grease, Shims, O-rings, As well as any replacement parts for the gearbox.
For the hop it is advisable to have a new bucking if you are servicing the gearbox since you have everything out already.
Shims are cheap enough. £3 a set. Get 2 sets so you have loads of extras.
https://www.ak2m4.co.uk/internal-parts/bushings-shims/shs-ra-shim-set
O-rings I buy in bulk. Do not get them from an airsoft shop. Get them from a bearing supplier. Expect to pay pennies for a single o-ring but also expect to have to buy more than 1.
There are loads of materials and hardnesses for rings. But for a standard AEG you want nitrile (NBR Or Buna-N are also terms for this material) and 70 deg hardness. In o-ring terms this is bog standard.
You have 2 options for the piston o-ring 19x2.5 or 20x2.5. 19mm is standard and fits like normal. 20mm is slightly oversized is harder to get in and wears faster, but gives a much better seal especially with problems piston/cylinder combinations, but the larger rings need a better grease as well. The added friction for the larger rings is mostly mute due to the way the ring expands and puts force on the cylinder walls, I have not seen a gearbox slow down for having an oversized ring in it.
Do not use oversized rings in ported cylinders.
Rings are measured as the
thickness of the band (2.5mm) and the
inside diameter (ID). Be careful on the order page as inside and outside dimensions can be selected in the menu options.
Typically it costs almost the same to have 2, 5, 10 and 50 rings. So it is universally better to buy 50 and have loads of spares that you can give away or store.
It might cost £3.40 for 2, £4 for 5, £4.50 for 10, And £5 for 50.
These guys do free postage on all orders. And will be able to supply cheap o-rings if you go for the 50 pack option.
https://simplybearings.co.uk/shop/Seals-O-Ring-Seals-NITRILE-O-Rings/c19_4501_4705/index.html
Grease is a crapshoot at best. Some on here will rave about some miracle grease that does all sorts of magical things. I'm not one of those people. For me there are 2 decent greases for an AEG. Soft Moly and Silicone with PTFE. These are the exact greases I use £6.50 for both. And they will last a lifetime.
Silicone with PTFE. For metal on plastic, and plastic on plastic.
https://www.ebay.co.uk/itm/SYNTHETIC-SILICONE-GREASE-WITH-TEFLON-50g-TIN-2HT-PLASTIC-SAFE-LOW-FRICTION/391399159157?hash=item5b21353575:g:4sYAAOxyuCJRbx-p
MOS1 Moly grease. For metal on metal.
https://www.ebay.co.uk/itm/Molly-MOS1-Grease-for-Airgun-Servicing-50-GRAM-TIN/173589020123?epid=650435926&hash=item286ab63ddb:g:tisAAMXQHU1RrnWG
Once you get the box open and post some pictures we will know more about what you need internally.
The bottom bearing/bevel gear popping is pretty common. They tend to get shimmed up to the pinion of the motor, but the other side doesn't matter so much since the motor is going to hold it. So without the motor it's pretty common to see movement on them.
The grease on the bearings is perfectly normal. Expect there to be black areas, Where metal rubs on metal even with a grease you get surface wear, and this colours the grease black.
For the upgraded barrel and hop unit: AK2M4 has you covered.
I'm a big fan of the ZCI plastic rotary hop unit for M4 platforms. You may have to file the ring a touch if it's catching on the front of the gearbox. A 45degree chamfer done with a file about 3mm in from the rear edge of the ring is more than enough and doesn't hurt the units function.
Again ZCI for inner barrel. There are loads you could pick on the market, but the ZCI is hands down the best value. And I don't think I've ever had a bad one. Avoid barrels with a coating, or alumimium barrels. Brass or steel only.
Hop rubber is sort of a personal thing. I love the prommy purples with those rotary units. Dropped straight in, no flat hop just standard on the mound with the stock nub. It's the perfect cold weather bucking alongside the G&G green.
The 50deg clear guarder are also o.k. If you want to spend more in the hopes of better accuracy go the maple leaf 50deg route. Keeping it soft will give you better winter performance at the cost of a little durability, but that isn't going to be an issue because you will know how to change it when it wears out!
