If the end of the bucking has got distorted I would of thought it was most likely from forcing the barrel too hard into the hop unit. Seen this done loads of times, you can push the barrel too hard trying to make sure its home and force the bucking lip to bunch up onto the barrel.
If you use a silicone mix oil some of the other ingredients can cause the bucking to perish or swell easier but pure silicone oil shouldnt cause that. The reason for not using it inside is because it will stay there and collect dirt and the nub doesnt work so well if its lubricated.