Some random thoughts...

When doing this job you should replace the tailshaft bushing as well. The bushing gets loose with age and causes the seal to leak. If you replace just the seal it might leak again very soon...

RE: The tailshaft housing - you are going to need to remove the driveshaft anyway, that will be a more difficult job than removing the housing. The only way around some of this is the puller that Rob mentioned. Check the 700/900 FAQ for a more thorough description of the job (same job).

Loose tranny pan bolts are probably causing some of your leak. Tightening the bolts alone should solve that problem. If you choose to replace the gasket, be careful and tighten in a cross pattern gradually for a good seal. I'd advise not loosening the drain bolt. More than one poster here on BB has stripped it so I stay away from that!!

Definitely replace the mount too while you're in there....

Running and MPG problems:
Check your knock sensor connection, I understand they can come loose sometimes. If your exhaust is that bad, it could be a clogged cat. Sounds like you might need to replace the system cat back anyway. A bad cat and leaky exhaust will also kill gas mileage....


Good luck and Happy New year!
--
90 244DL about 1/4 million miles - original engine/drivetrain :)