Malfunctioning Camera Ruins 6 Rolls Miraculously Becomes Normal Again

My X-700's shutter was firing of at likely 1000th a second reguardless of it being set for both a 60th, then a 125th for 6 weeks and 6 rolls of film at a noisey construction site 2 Summers ago - that's why i didn't notice the quicker then I'm used to ka-chung. Wiring and/or circuitry thing or something need fixing. My neg's were faint to clear, grossly Underexposed.
Not until now do I decide to get it repaired so I toy around with it before shipping it off and lo-and-behold, it works as if nothing was ever wrong. What went wrong then? What's right now?

Electronics failure. Solid state devices sometimes have "self healing" characteristic, it fails, sits unpowered for a while and on cooling the crystal layers rebond and the component stars working correctly again but will eventually fail, the question is when.
Sometimes electrolytic capacitors self heal but fail soon after.
Use it until it quits then get another.