Pop that plug out; it's the plug to access the drain plug for the TC.
If fluid pours out, that's bad.
It's normal for the front and rear main seals to leak, at this point.
Front leaks on heavy breaking, rear on heavy acceleration. (or jacking, lol.)
You have to pull either the engine or the transmission to replace it, so...
See if the TC drain is leaking; it happens.
The shifter linkage is covered, so that probably means the shaft seal is leaking.
Grab the DS, and try to turn it while looking carefully at the u-joints; movement in any of the bearings is a problem. Check both ends.
17 year old seals are the problem; Time for upgrades!
You can rebuild the tranny, but there are better ones to do that to.
You could rebuild the engine, but the same thing goes.
Note: If you can rebuild one of these for less than $1k-2k including machining, you are an Ebay Master, lol!
I buy 02 trannys, then hope to rebuild them as I wear them out.
The 03 PI swap was much cheaper than a rebuild; it had 725 miles, lol.
The Teksid block on my stand is worth rebuilding, but Man is that a lot of work.
The next one I won't take the lower end apart; every one I've disassembled has still been within factory specs. I'll replace the seals, and go with new heads.
Just be aware there are 3 stock piston sizes, with about a gram of weight difference between them; not the best thing for a race engine. Or Nitrous.