That sucks indeed!

Regarding that chain: I've been told by my shop guys that there is such a thing as too much lube. Unless you also clean it thoroughly every time you lube it, the lube will actually help the nasty stuff get into the depths of your chain's links and increase the wear and tear. Now I'm more careful about oiling the chain, but unfortunately I don't always have the time to thoroughly clean the bike, especially in the winter when it would be every day.

About the wheel: I hate to ask, but how heavy is your DH? I know that in road cycling the weight limit on most wheels is 170 lbs, beyond that they don't guarantee them. Of course on a mountain bike you'd expect the wheels to be sturdier than on wheel bikes. But I'm wondering if that could be a factor for you, and if sturdier wheels could help.

Definitely not a happy day for you at the bike shop!!