Can't focus to infinity with my 135mm f/2L!!!

I did some tinkering with the lens and managed to get it to focus to infinity again. Turned out to be the outer o-ring screw. I'm not sure if that's what its called, but its the ring that screws over the front glass and holds the front glass in place. It has 4 notches on it for a tool to fit and screw/unscrew it.

If I moved the lens around, it always made a very soft, damped "clank" sound, as if something was loose. I always assumed it was just the focusing ring moving slightly, as I have had lenses with slightly loose focus rings that made almost the same sound. But when the lens started having focus issues, I thought it'd try and tighten the front ring, since its really the only thing I could do without taking the lens apart. Sure enough, it was loose. I tightened it. The lens no longer made that clanking sound, but it still didn't focus to infinity.
 Couple of months later I loosened the ring again, just enough to get that "clank" sound again. Then I grabbed the lens in my hand and gave it a few good sudden twisting motions, in the hopes that maybe whatever was loose inside would thread up or down to where it was supposed to be. Put the lens back on the camera and... it was working fine! Then I tightened it up again to keep it from moving.

I don't know if it was just crazy coincidence, or if my assumption that there was something that needed to thread back into place was correct, but I can focus infinity again.

I didn't have the tool to tighten/loosen the ring, so I used the nail filer from a nail clipper. put it into one of the notches, and turned carefully. I could have used a small flat screw driver, but it stuck out a bit much, and I was afraid of it slipping and scratching the glass (be real careful if you decide to try this, the nail clipper slipped from the notch a couple of times, and each time I was sure I put a big scratch on the front glass. I was lucky I didn't)