Clutch problem comes with surprise.

[Pushit2.0]

I have had and seen disk problems with these cars a lot. Buy a new high quality disk or clutch kit. Mitsubishi stock, or OS/Giken based clutchs are all good options. I would think someone pulled that plug out at some point and did not put any sealant on the threads and/or did not torque it to spec. I would take that plug out (8mm allen) use plummers dope and torque it to 33lb/ft.

~John