Replacing the valve seals is not that difficult. The most complex tool you need is the type of valve spring compressor that hooks on the cam.

Don't worry too much about the valve guides. If they're really worn and oil consumption continues or comes back shortly, all you lose is ~$20 in parts and an afternoon. What you gain is time to shop for a good deal on a full valve job.

Sixto
91 300SE
87 300SDL