The plastic panel is not an issue to me. I've seen plenty of those broken and broke one or two myself. The spots on the floor under the car may be an issue. If it is a Rear main seal leak, or IMS seal leak, the transmission has to come off to replace/repair it. Many of us have done it as DIY, but not a good starting point for a beginner. Lots of labor cost at a shop. Good opportunity for a clutch and replacement IMS bearing though.
If the price is right, it would certainly be worth having a knowledgeable shop do a PPI and estimate on.