Don't pull the head before investigating further. The valve seals really were a problem with this engine, but the head does not have to be removed to replace them.
If you don't have records, find someone in SoCal thoroughly familiar with the breed, who can pull the valve cover and tell if they have been changed. I don't know if anyone can peak through the spring and tell, but I'd find out before I pulled the head.
My 300E came with complete records and the valve seals had been replaced sometime well before 88K miles. The engine now has 170K and uses so little oil that it's almost scary. So I know that it can be done.
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in