If it's a perpetual motion machine, then by definition, it is capable of going on forever (within human error, I'll give you that). If you are extracting mechanical energy from it, then there is no avoiding it: you must get this energy from somewhere. There is no source of energy which is completely inexhaustible. You may have explained this before, and I misunderstood you, but is this truly a perpetual motion machine in that it can, in theory, continually produce energy forever, or do you mean it can draw from an energy source which is, in all practicality (but not theory), endless (such as converting the mass from some other galaxy into energy or whatever)? If you are not drawing from an exhaustible source, then you must be getting energy from nothing, unless this is the entire basis for your machine. It's too bad you can't tell us more details, because I'd be really curious to learn where exactly this energy is coming from. I don't blame you for not providing more information as if I really thought I had come up with such a device, I too would be careful as to whom I gave this information, but you'd be a lot more likely to learn what is wrong (or we'd learn to what degree we misunderstand physics) if you would provide more information.
Either way, good luck.