While reasonably plausible, that is a far, FAR cry from being prosecuted for merely owning an oil filter as you claimed when you posted: "According to the letter of the law, they CAN charge you with illegal possession of an NFA item for owning an oil filter."
The person in your intricate scenario is NOT being prosecuted for "owning an oil filter". He is being prosecuted for buying something that's one hole away from being a silencer, attaching it to his gun (requiring threading the barrel and purchasing or making an adapter), and then putting a hole into it, making it fit the legal definition of a silencer in every respect. In other words, he's being prosecuted for owning something that is totally indistinguishable from an illegal silencer (and which therefore IS an illegal silencer), not for merely "owning an oil filter".
To make this happen, the guy in your story had to buy the oil filter, buy the adapter, thread a firearm barrel, attach the adapter to the gun, attach the oil filter to the adapter and then shoot a hole in it. Shooting a hole in the filter might have been an accident, but everything up to that point was essentially impossible to do by accident. In other words, anyone who wants to avoid being prosecuted for this sort of thing can easily manage to do so.
Do I agree with the silencer laws and how they're enforced? No. But let's not be ridiculous about this. People aren't being prosecuted for merely owning oil filters, nor is there any danger of something like that happening.