1993 940 sedan, 165,000
Oil - Front main engine seal replaced ~5K ago, looks like rear main still dripping.

Tranny - Mysteriously, the trans fluid was almost empty, resulting in a lot of slipping, etc. However, I haven't seen any significant dripping in the garage or my ususal spot at work. Any ideas on how this fluid can mysteriously disappear? Also, should I use any additives to the trans fluid to offset any potential damage from when I was running low? It ran low for about 1 week before I got it taken care of.

Rattle - Muffler replaced last December. Recently, I get a rear end rattle, however, its really only noticable when I have passengers in the vehicle, and, its audible when sitting still. It quickly goes away once acceleration begins.

A/C - Blows cool when moving but air is noticably warmer when sitting still. Is this the Heater control valve?

I'm not a realy DIY'er, but would be willing to try if I can reasonably expect to successfully fix any of this on my own.

Thanks for any/all help.