I have been searching the forum but have not found specific recommendations on age/milage of replacing the tensioners for my car (03 str) what are the recommendations as I'd like to head off any potential problems-thanks

 

There shouldn't be any need to replace the tensioners on your car.
All the earlier problems had been resolved by 2003.

 

Would you not change them when changing the chain, guides, etc? hmm, which goes (as in: needs replacing) first?

 

I expect you would if something was failing, but they are not a maintenence item like they were with the 4.0s.

 

Do the guides wear / get brittle and fall apart first? Any idea when?

 

I've not the foggiest, I don't recall anyone having tensioner problems with the later cars, do you?
Even with the 4.0 cars most people seem to just replace the uppers, those that do the lowers usually report some kind of deterioration of the sliders.

 

You've got me - no, all seem good. Maybe no-one's done enough miles yet!