Thanks all for the replies - I'm on different shifts from mate 2 (knackered v8) but have suggested checking plugs and leads (thanks for that) to Mate 1 (S2, not blown up yet) along with compression testing.
Must admit for a relatively low mileage car (30 odd k) for the liners to go it must have had a hard life, or my mate is just unlucky and and buys nails (saying that, he is on his 2nd impreza turbo engine in his daily hack, having blown up the first on a track day... hmmmm. Pattern building...)
Thanks for the help - will advise on progress.
Ah yeah, forgot to add, the top of the eng