Glad to hear that you were able to repair your leak, also that the dealer DID get back to you be it late.
Water hammer is annoying and it sounds like you have tried all the fixes.
I installed a accumulator tank on our previous coach. What I did was go to Lowe's and buy the 2 gallon tank. It did help a little with the hammer, but what I really liked was the fact that the pump didn't run as often, but when it did it ran longer to fill the accumulator back up. Therefore it seemed that the hammer didn't bother us as much. The wife really liked it because in the early morning hours I could use the toilet and flush it without the pump ever running. It didn't wake her.
It also stopped the pulsing in the shower from the pump pressure variation.
The 2 gallon at Lowe's is much better than the smaller RV version. I made a bracket to mount it on the wall under the bathroom sink in the cabinet, but can be mounted anywhere there is room and access to the cold water line. I also installed a valve so that when I winterized I didn't have to pump antifreeze into the accumulator.
Ron