Yes, it depends on what transmission, some used motor oil, some used gear oil, some used Automatic Transmission Fluid. Make sure you use the correct juice!
Unfortunately it did not come with a manual. I did see a video regarding removing to lower hoses but not exactly sure. And also concerned about what fluid to replace
Its recommended you suck it out of the filter opening. Do it warm, to get all the contaminants stirred up and out of the transmission. Pull the plug at the bottom and put a pan underneath (you will need a pump to suck it out of the pan as there might still be a good amount of fluid in the bottom. Sample your gear oil...it about $20 per side and you can get an idea of and track the health of the trannies.
Filter opening requires a 6mm hex. Loose up the bolt, and pull the whole thing up and out. You can wash the filters to see whats in them, and if you choose, reuse, but I replace with new. Filter kit comes with filter and 2 orings. and are cheap ($36 on ebay).
Once empty, I installed a valve and a length of hose with a garden hose fitting on the end. Matched up to a cheap ebay pump screwed onto of a 5 gallon plastic bucket make super quick work out of this job. I can now do both transmissions in an hour.
I aso use Mobile1 Synthetic ATF. Summit racing has it for $31/gal w/ free shipping.
On a ‘98 330, you’re looking at BorgWarner Velvet drives if you’re running 7.4s. That’s what I have. It uses ATF. Easiest way to drain is to pull the pump line going to the cooler. Should be on the port side. I’ve had a few tranny issues, and this is the quickest way to drain them.
If you don’t know the age of the coolers, I’d look at replacing them. I had one go out on my starboard side, filled the transmission with seawater, and I’m now in for a transmission replacement. It’s about $150 for peace of mind.