You could try KB Motorsports in San Marcos - (760) 471-0441 the original owner was super cool and not afraid of diesels. We took my ‘85 and ‘86 TD524’s there, and my dad would order parts for his diesel VW Rabbits there. When Kip retired his main tech Vlad bought the business, guy is very sharp and a great mechanic. I haven’t been there in a while because I haven’t been driving a German car, but I did call a couple months back to get some info.
If they don’t do what you need they will probably know someone reputable who does.
There are a couple other places in the area that have VW/German ties, but I’ve never had them personally work on my vehicles so unless you want to check them out, I’d rather not mention them and send you to a bad experience if they don’t know diesels.