2012 was possibly when VTs were back door Inokatsus and I believe there were some issues. VT has come a long way since then and have been refined a lot. King Arms mags are pretty much 100% clones of WA mags which are notorious for leaking. Depending on how many mags, £350 could be alright. Perhaps get on to the GBBR Heavy Recoil Club on Discord. Lots of very knowledgeable people on there.
Spare parts are available from some HK shops or VT direct. By all accounts, the recent VT GBBRs are considered the creme of the crop of GBBRs. Though like the early Inos, if you get a bad one, they can be money pits.