DON T. - I'm not really sure what the sealer IH used on ALL castings really was. We've dicussed it here many times. The castings were all "DIPPED", never sprayed, so interior as well as exterior surfaces were coated. And it's completely impervious to any petroleum solvent that I've ever tried. So Brake-Clean, diesel fuel, kerosene, gasoline, are all good to clean up the inside of a CC rearend. I'm not sure how it responds to things like lacquer thinner, acetone, etc.
The sealing was actually handled by outside painting/dipping/sealing companies for IH's foundries. Back when I had a foundry or two to chase parts out of I actually had to call the painting co. to get the day's shipments to know if my hot parts shipped.
THAD - I've been into the lift handle once or twice on a #72 which should be the same as your 105/125, but that was a few yrs ago. About all I remember was that I didn't take the chrome part of the lever off the bottom end of the lever, It's welded solid. If you remove the entire rock shaft, and also the lift quadrant the bend on the bottom of the inner rod engages to let the rockshaft hold the mower/etc at different levels, you can push the inner rod up far enough to remove the top button with a pair of pliers, a vice grips, pipe wrench, etc. Just be careful you don't twist the end off the top threaded end of the inner rod. They were No Longer Available as separate repair parts even when the tractors were brand new. You had to buy the whole rockshaft assembly! You had to make your own inner rod from a piece of 5/16" rod, threaded on the top end and cut to the proper length, and installed down the lift lever, then heated with a torch and bent so they engaged the lift quadrant again. The top button, the float locking button, the spring, and special flat washer are still available from the sponsors above, the colorful boxes are links to their website.