Hello! Sorry to hear about that! What usually happens, is the checkvalve deteriorates over time and allows some exhaust gas into the air tube. Water vapor is a natural byproduct of combustion (which is why cars smoke when started and its cold outside and water drips from the tailpipe). That water vapor condenses in the air tube and goes down to the pump, which can rust the insides (seize) or short out the electronics, both of which require pump replacement, and they reccomended the checkvalves to prevent future failure.
If your handy with tools, you might be able to do it yourself and purchase the parts from an aftermarket (reputable) part supplier like www.eeuroparts.com (I think their website is currently down at the moment, I tried to look it up for you).
I don't know of anybody who rebuilds them, but its basically just an electric motor, so if you know of anybody who rebuilds electric motors in general, they might give it a try.
Please let me know if you have additional questions!