Hi Gus,
While you may never get the minute accuracy of a quartz clock, a respectable time telling instrument can be achieved. Like most things mechanical, your clock probably suffers from years of dust and dry lubrication. Clock lubricants are very light in viscosity and used sparingly, yet it's application certainly lends to accuracy and smooth operation. The folks at Palo Alto are quite respectable and honest....I think a call to them will answer your questions.
I would also perform a good search on this forum, along with the other Mercedes sites, for discussions on mechanical/electrical clocks. While I haven't tackled mine yet, I do recall postings discussing how to clean and service the clock yourself if you are so inclined.
I know many vintage car owners who have converted to quartz movements and never looked back (after all, the clock will end up looking the same). Yet others, like me, prefer the charm of the original instrument with it's noises and quirks. But that's a choice you'll have to make. Good luck!
Best Regards,
J. P. Mose
1968 250SL
1987 560SL