aah. Your out on the west. I dont know anyone out there. closest is Layton, Utah. sorry.
Follow the recommendations of others here as to the fuel tank, fuel filters, ect.
As for the transmission, its not a single seal, its a dozen or so inside, no simple replacement. I would first take care of your sick engine, then when thats solved, focus on maintence of the transmission
You can tell alot by the color of the fluid on the dipstick. with the engine warm and idling in neutral, check the fluid on the dipstick. check it for color and appearance. sniff the dipstick. compare all these properties to the color and smell of new ATF. If the transmission fluid is brown, smells burnt, or has alot of shiny particles in it, you need help. If it is just slightly darker than new ATF and smells the same or very close, your fine. If its clean in the transmission, I'd feel safe just changing the fluid in the pan and the filter. If the transmission stuff is dirty, i'd just leave it alone. If its pretty clean, your probably safe doing a fluid and filter change.
Good luck fixing your car!
2003 Jetta Wagon TDI 145,000MI
1999.5 Jetta TDI 287,000MI
2001 Suzuki SV650S 26,000MI
2008 Yamaha Vino 125 11,000MI