Yes - Paul Anderson is notoriously hard to get hold of but then he is never short of work either due to the fact that he knows the 928 inside and out and is competitively priced. [no affiliation]
I took my 928 to the other top 928 garage last October [Loe Bank] and faced a similar problem. They we're totally swamped with work and as I gave them the impression that the job was not that urgent they took over 2 months to finish it, but it was expertly done and at a fraction of the cost of a main dealer. However, the money saved was off-set by the cost of having to have the car trailer-ed there and back. (£250)
Sure, you can take your 928 to your local Independent garage who 'say' they can look at it straight away but have never actually ever seen or worked on a 928 - just imagine the consequences - even jacking up the 928 incorrectly can damage it. The long term costs could be astronomic.
It's all a bit of a gamble unfortunately and a problem that's only going to get worse as the 928 becomes rarer and rarer and Porsche mechanics who have actually worked on and know the 928 retire.
The best plan is to find the all Porsche garages that are closest to you and then go by recommendations from this and other forums.
Ben