Exactly 300,000 on a passenger car or in the case of our family van is not uncommon. Heck these even a Camaro around here that has 500,000+ on it.
As for $300 I would never pay that much to get a valve job on an inline 6 you'd have to be crazy. I'm paying $180 to get a complete head rebuilt and have hardened exhaust seats put in. The fact of the matter is they were going to have to be replaced anyways why not pay the few extra $$ for hardened seats....
Also john the exhaust seats on my 6 although beat into the head still showed fine compression on all those cylinders so even though you went 100,000 plus doesn't mean there isn't damage there.
