Has your car had any valve work done?
Early M103's had soft valve guides that wore rapidly, and if this is the case with your car, I'm not sure if new valve seals will help all that much. OTOH, replacing the seals is a heck of a lot easier and cheaper than a valve job, and if the seals have been in the car 16 years, they've probably lost a fair amount of the sealing capacity anyways.
FWIW - had valve seals done on the '87 and '91 when both were burning about a qt every 800 miles or so. That helped reduce oil consumption to about 1200 miles, then I switched to a higher weight oil (from Mobil1 10W30 to Delvac 1 and now going to M1 15W50) and now it's about every 2000 miles. Don't know exactly why, that's just the way it happened.
2000 C 2 3 0 Sport :: 180k