yeah, i think there may not actually be anything wrong with the rcd at all. I've come across types, and expect that it is as such, where the rcd has an internal relay that closes when the rcd is reset and opens when the power trips. however, because of the construction of the relay [it's probably got mechanical/push button closure only] it is impossible for the relay to reset itself after a power failure.
The ones of this type that I have come across are inline rcds for use on extension leads. when ever you put the lead in a socket you need to reset the rcd as well.
so, the rcd isn't actually faulty [unless you just absolutely cannot live with an rcd that operates like this- then it may be easy enough for a sparky to replace] and all i'd recommend is that you don't have anything that cannot go without power a an extended period of time [fridges, freezers, grandma's life support] connected to the circuit.
however, this is just speculation based on what you told me and may be wrong.