Speaking as someone who uses Mach 1 (and Powersports) rather religiously, I've never had a problem with any service and support from them. As a matter of fact, I just picked up my FZ from them on Thursday from a bent rim and new tires. Yes it's a busy time of year and they are swamped for the staff they have. I think they've also had some service staff changes recently so it might take the new people a bit to get into the swing of things.
First, thing I wanna mention... it's kinda bad form to name a shop without at least giving them a chance to make it right. I once did something similar and didn't even name the shop and in retrospect I felt like an ass over it.
Second, Jeff Leggitt is a great guy. If you call or go in and ask to talk to him he'll be happy to work with you to make it right.
Seriously though, I can understand the frustration but as you said yourself it is the height of the riding season, the economy is kinda screwed up and as I mentioned there's new staff on top of that. While it sucks that you're out $500 and your bike still leaks there is always a reason for things. Oh and $500 is actually not a bad price considering a new pan and pump gasket were installed. Just talk to Jeff. I'm sure he'll work with you on it. He's been in business for years and you don't stay in business if you don't take care of your customers. Particularly in a smaller town like Vallejo with all these cities just a few miles away.