Sounds likely then.
Best test to be sure (assuming you can drive it at the moment) is to put it in 5th and floor it at about 30mph, as the boost comes in around 2000rpm onwards you'll see the revs flare and feel it slip. Worth double checking.
Could be contamination on the plate / flywheel, but then it's probably an engine out job to address that anyway.
For the record though the clutches last extremely well on these. Last time I changed mine I regretted it really (only did it as the engine / box was out). Clutch looked brand new after nearly 90,000 miles, and the one that went in isn't as nice
You can put an A610 clutch in, makes it a bit heavier as it lacks the helper spring but I've always stuck to standard turbo clutches. Good luck - you'll be fine. If you've done clutches before then the GTA isn't really that tricky, the whole rear assembly will come out on the subframe as Lee said, or you can go the engine out via the hatch as John's pointed out.
I'd go the former as it then gives you access to the whole running gear if you want to replace anything while it's on the ground. Also putting the engine back in via the hatch can be a tricky to make the splines align, I'm sure John probably has a trick up his sleeve there (plus he has the patience of a saint as we all know since he can fix French electrics and put up with us lot
)
I'm just here for the gasoline.