I think they are pretty easy to rebuild. Finding parts is the hard part. Most of the pressure washers sold now days are cheaply built and considered a throwaway.
That's what I'm doing now- trying to find parts (vendors) for it. It's a Northern Tools unit with an upright (horizontal shaft) Honda engine with what I think is a Comet pump, but it would be a helluva lot easier if I knew for certain, as I'm going by pictures (and visual memory) at this point. And my wife isn't home to get me any numbers off of it....
If I have the time I'll dig into tonight, and if I can find parts for it: Great!