Tom,
There are two good independent shops that have experience with W113s and other Mercedes from the 50's 60's and 70's.
MBI Motors: 503-231-0444. A Portland institution, been in business for over 40 years.
Burback Motors: 503-236-1737. Owned by Mike Burback who spent time at MBI. I take my car there.
Contact me by PM if you have further questions or want to discuss.
Cheers,
Allen