Yeah, it’s overkill, but here’s the thing: the first time I did this, the abundance of oil freed up a bunch of nasty old beard trimmings that had apparently been lodged deep inside the trimmer head, stuff that wasn’t even visible. Immersion, apparently, floated that junk out. It was revolting, but it’s also nice to know that the sucker got fully cleaned out.
Umm, how do you tell when the oil is gone? I’ve got a Remington that probably should be oiled. What difference does the oil make?
Listen to your clippers pre and post lube. The difference will be obvious.
I believe the manual says lube every 6 months or so. I usually do it when they so noisy I notice.
If you DON’T say something 
??
BTW, my clippers manual says to use mineral oil. Walmart, buck fifty per pint.
I give my clippers an occasional squirt of WD-40. A drop or two will last for several months.
Actually, my friend had a horse, one of the pre-show jobs was to clip the beasty’s coat.
The either Wahl or Oster clippers she had said to do exactly that after each use to get that hidden stuff out of the clipper head (which unlike most beard trimmers requires a screwdriver to remove).
Given the prices of some of those clippers, it’s probably not the worst way to clean beard trimmers.
CMC +fnord!