Anybody else do it? I make them pretty often, generally out of necessity. I found that the standard spool seals do not exert enough force on the valve body bore to create a positive seal. I am speaking with regards to the bendix style truck control valves. For the spool seals, I took my hard old ones, chucked them in my vertical lathe (drill press, bolt and file), and filed a little grove to fit an o-ring. I made the o-ring protrude a good 1/32" or so from the diameter of the seal. It took a good snap to get them in, and they seal so well, I replaced my other new ones, that were weeping a little with these. I did the same thing for the other o-ring sealed components, and now the valve is perfectly sealed, and didn't cost me a dime. Hope this helps somebody.