Hi Paul,
We had a 2007 Subaru Legacy 2.0T in recently that when cold would stall pulling up to junctions and had rough idle until warm, we did all the usual checks then checked tappet clearance <0.1mm on the exhaust but these dont have shims (the whole bucket is the shim) so heads off and had valve ends machined to bring back correct clearance (due to exorbitant cost of buckets and dealers taking days to get back with prices) Sorted the problem but what a pain thought cust might do the usual and trade it in (btw gaskets individually £200!) Glad to see he didn't off load the problem to an unsuspecting dealer!
I didn't look through the serv schedule for the Subaru but wonder if they or Renault state to check at any point probably not, if irc Alfa use to list tappet check in their schedules
Rob