Hi,
I just bought a Miranda B which had a split in the second shutter curtain. After firing the shutter a dozen or so times, the curtain parted company with itself. Apparently the B is a fairly rare model and mine is in excellent condition apart from the shutter. Apart from the fact that I don't know who would undertake a shutter curtain replacement, I suspect that if I did find someone the cost would be far more than the camera's worth, though perhaps that's not the case with your Miroflex. I do basic repairs to SLRs, though I've never delved quite as deep as shutter curtain repair. However, there's plenty of information on the web about the techniques involved and though they tend to relate to Leicas, Zorkis etc., I don't imagine that the basic principles are too different between FP shutters of that vintage. I regard it as being a job for the long winter evenings and if it should go seriously wrong, my 15 Miranda will have to suffice as a display item.
Best wishes,
Steve