89 420SEL check light

[SNBmerc]

Just had to reset the computer again - checked and got 12 flashes (indicates EGR sensor I believe - anyone confirm / correct me ?). That's the second time I've had this code, the last time was January '04 / ~128000 miles which makes it a ~22 months / ~12000 mile interval. Is this a common occurrence or am I looking at some (long term) problem ?
By way of additional information, the motor pinks (pings ?) quite heavily when hot and number 4's spark plug shows evidence of being the most significant oil burning cylinder - the rest all look quite healthy (motor burns ~quart per 1100 miles). Wish I could do something about the pinking - I've already had an MR2's motor destroyed that way - don't want to repeat that with this car :-(.
Any decent places in San Diego where I could have it checked out ?