QUESTIONS: Changing ATF, oil, and diff oil

[JonathanS]

OK, folks, I'm set to spend part of my 4th of July weekend under the SVX. I have a few questions.

Motor oil: I'm adding a Fumoto valve and switching over to synthetic (Mobil 1 10W-30) and a K&N oil filter. The former owner's husband told me that he put in synthetic some of the time, so I am hopeful that I won't see too many leaks. Amsoil, which makes an engine flush-in-a-bottle, recommends flushing before switching to synthetic. Red Line, which does not make a flush-in-a-bottle, says it is not necessary to flush the system. I don't want to dump any old harsh chemical brew in there, and I can't find anything better than "Gunk." Should I skip the engine flush and rely on Mobil 1's detergent mix to clean up anything that needs cleaning?

ATF: I'm going to drop the pan, change the internal filter, and add an external filter and a tranny cooler before filling it with Red Line D4 ATF. I plan to drain according to Amsoil's 12-step instructiosn, which sounds like it will get at quite a bit of the old ATF. I don't know for sure what the previous owner had in there before, but I assume it's dino ATF. I was planning to pick up some Lubegard ATF Flush last night, but the NAPA store that told me by telephone that they had it turned out not to have it. Here's my question: Should I stop worrying and take Red Line's advice (in other words, skip the flush-in-a-bottle step)?

Diff oil: I'm confused. When I ordered my Red Line ATF, I also ordered a quart of the Red Line 75W-90 gear oil for the rear diff. The front diff, however, calls for 80W90, which Red Line doesn't offer and which I can't find in synthetic locally. (I don't want to pay $9 in shipping for $18 worth of Amsoil or Royal Purple synthetic 80W-90.) Should I go with dino 80W-90 or change to a different viscosity grade (75W-90) in synthetic? Or should I just stop whining about the cost and get the Amsoil or Royal Purple diff oil in the recommended 80W-90 grade? Hey, I said I was confused!

Are there any other fluids I should be swapping out while I am getting greasy under my new-to-me 1996 LSi with 76K miles on it?