fluid change

[suprastarr]

I'm looking to change the fluids(transmission, differential, and power steering) in my 86 but I'm asking a few questions first!
1. What fluids do you guys use and what kind of fluids would you guys recomend?
2. Should I use any additives?

And on a side note I was considering a engine oil flush but I've got an oil leak and was worried thet the gunk in the engine is what's stopping the leak from getting worse any thoughts?

By the way I have a stock 4AC.

[BriscoMedia]

I just did my oil yesterday, I used 5W40 T6 since it has the highest zync rating. Would recommend it! As far as tranny oil, I think we use Redline MT-90 in the shop.
If you use regular engine oil, try using a Zync additive.
Have you found where the leak is coming from?

[dr.occa]

Been a faithful Castrol GTX conventional 10W-30 & Pennzoil Syncromesh for trans user for decades.

[milchmann]

I personally use Motul for the trans and diff, and MobileOne for engine, but honestly, your best off using the same thing regardless of brand time and time again as soon as it is rebuilt rather than worrying about what is "best" and changing things up. Using high dollar stuff in a clapped out diff that has seen nothing but generic fluid its whole life will probably give you a nice high pitched whine until you rebuild it.

I also typically use extended mileage oils and still replace them every 5K/6 mo. and a neodymium magnet drain plug.

As for the oil flush, do not do it. If you have a leak, find where it is and fix it, and then change your oil twice in one week (one of those will probably be taken care of when you replace the offending gasket). All oils you can buy at the auto store have detergents in them, and running one for a week will clean out all of the buildup you need to concern yourself with. Flushing out too much contaminant should definitely be a concern, but it is more a problem for friction parts such as bearings/journals/gears/syncros than for leaking gaskets which are easier to replace.