My right rear side of my sl55 starts to sag after sitting for a couple of hours. I'm pretty sure my car is due for a valve block soon. A replacement is around 2k on fcp euro. However, I could try to repair it for much less than that? Does anyone live in the Bay Area/San Jose that knows how to repair this? Also, if anyone has opted for the repair, how is that holding up? I'm not to mechanically savvy so recommend some places that can repair these. Please send some tips and advice, thank you.

The following should save you serious money. As long as the valve block hasn't been upgraded by a previous replacement, this should work. I don't know anything about this link or company, but I've read good stuff. The web site alone describes the valve block issue in great detail and at least I understand it now. If I have an issue on my 06', I plan to use them, though since the front and rear are the same p/n, I may try to find a decent core to send in and get it rebuilt to put on the shelf. Would save time on the rack.
https://www.diybenzrepair.com/

My understanding is if the valve block is function fine the new seals will last a long time(10 years or so). You could always call around to some independent shops that work on Benz's and ask them what they'd charge to replace the valve block seals. I'm sure most shops have done this multiple times for customers.