My friend got a WRX earlier this year. After he owned it his clutch went out and he replaced it. Ever since it has had chatter. As of late it has gotten bad. He is going to take it apart again soon. The only thing I could think of is maybe the rear engine seal is leaking a little oil.

Anyone have any ideas?

What sort of clutch is it? Some aftermarket clutches will chatter .. thats normal. Ask him to search/ post on nasioc for more expert advice.

But RMS leaks are common, and a common cause of clutch failure. I had one of them in the old Legacy.

Did he replace his flywheel? Or at least have it resurfaced? Thats also a good source for clutch chatter.

He did replace it with an aftermarket Clutchmasters disc, and he did had the flywheel resurfaced. He said he is going to replace with an oem disc.