So my 98 gs300 has weird rectangular rubber plug like thing on the front of the housing where the engine meets the trans. I have no Idea what it is but there's a good amount of oil leaking from it. Can anyone identify what it is?

 

Oil Pan Inspection Hole Cover.
This part is a rubber cover for the upper oil pan inspection hole.


From Driftmotion's website

 

That would be it, do they go bad or something? It appreaded to be all the way in but its still leaking pretty good.

 

Its an oil pan inspection hole 'cover', all it does is cover the hole. If theres oil around it, then its probably coming from what this hole is made for inspecting... The oil pan.

 

The hole isn't actually for inspecting the oil pan, it's for accessing the torque converter bolts. The cover prevents road debris from getting in the bell housing. The oil is coming from a leaking seal (e.g. rear main seal) and gathering in the bell housing until it drips out.

 

^This, what he said