MBG motor puzzle

[rfl@yerkes.uchicago.edu (Bob Loewenstein)]

I'd just like to add my experiences with the burned exhaust
valves of #3 cylinder. My 65 B has about 175,000 miles and
every 40-50k I've had to do a valve job to take care of that
#3 valve. I'm due for one again. After the second time I did
adjust the clearence a little out of spec to ensure that the
valve would close. I don't think it helped.

Do I detect a pattern?....