Either your mechanic put in the wrong valves, the machine shop did not use the correct metals for the valve seat repairs, or the oil/coolant passages are clogged. For the last one, it could be that sealant used in the cam cover may have been put on too thick and covered some of the holes around cylinder #2.

None of the above is your fault. Using hotter burning 87 octane in your LPT for 30,000 miles didn't cause it either. Highway driving, under 3000 rpm, with 87 octane shouldn't cause any problems, the hotter 87 octane will cause trouble between 4-5000 rpm. I see no concern for those who use 89 octane and like high rpm.

Why would you need new valve stem seals? They are typically good for 200K+.

--
Keeping it running is better than buying new