The arm lift cylinder contains very thick goop that allows the lift to rise and fall slowly. When the stuff dries up or leaks out, the result is fast dropping. You need to remove that cylinder, disassemble it, clean it, and apply new goop, and that should be fairly easy to figure out on the 12D.
The irony of all this is that the only audio place that carries this goop, called silicone damping fluid or oil, is turntablebasics.com, the place I told you to stay away from. The stuff comes in different viscosities. You'd need at least 300,000 wt. (300K), but possibly higher. My PL-570 uses 500K. But even if yours needs that too, if you put on enough of the 300K it will probably work. Look online or locally at radio control hobby shops for 300K or 500K "diff oil". If you can't find it, you'll have to take your chances with turntablebasics.