A good buffing wheel will work wonders on an oxidized stem, and shouldn't abrade away as much stem material as sandpaper or steel wool (use #0000 if you do this). Get the lowest-speed buffing setup possible - a jewler's wheel is best, but a lowspeed bench grinder will work in a pinch. Keep your polishes apart - use different wheels for each, or they'll become big, gummy messes. I use Tripoli brown, white diamond, and carnauba (NOT car wax...buy a stick of pure Carnauba at a woodworking shop). The brown is aggressive, and will clean up anything. The white diamond will take care of most stems. The wax is just to put a coat of nice, shiny wax onto the stem and/or bowl if you like.
If you put a vulcanite stem into bleach, it will clean it up like crazy, but leave it gray/green with oxidation - so you'll have to find a way to buff that off.
As for tightening stems with heat, here's how you can do it: GENTLY, and SLOWLY heat it up over a candle - not too close to the flame; you just want to slightly soften the tenon. Once it's a little soft, (again, GENTLY) push a nail into the hole in the end of the tenon. This will expand its outer diameter. If you go too far, it won't fit....so be careful and do it slowly. You can also put some beeswax onto the tenon and reinsert it. When it heats up & is absorbed into the briar, it will eventually tighten it up - may take a few passes.
Estate lots are a great way to get some pipes you don't have access to otherwise. If you like old, quality briars, they simply aren't made today (there are plenty of good briars today; just some makes/models are no longer available new). So, you're left with getting an estate example. Pipemakers that have died, lines that go off the market, etc. will be other reasons you can go that route. They will sanitize and clean up to look brand new if they aren't too banged up, and it gives you the opportunity to smoke some cool stuff. I've gotten nice old Dunhills in estate lots before with less than $5/pipe invested. I used to buy big lots, clean them up - then sell the ones I didn't want. I often got some killer pipes this way for free - selling the less desirable ones often pays for the ones you keep!
