I made a few flash units, they're just xenon strobes with a Cap and a trigger coil. The real problem is sourcing shielded wire. The voltage from the cap is so high that it'll arc through normal insulation. I got some pretty nasty shocks messing around with them, I decided it wasn't worth screwing around, they aren't your normal zap you might get from an appliance, etc.

Tamiya has the cap in the MFU itself, not the flash unit. Caps themselves have a limited life and believe it or not, they're so predictable that most electronic warranties are based on the caps. If they warranty for one year, some dubious companies will use caps built to last for a certain amount of time to cover that year.

In all my Tamiyas, I've only had one get weird on me, it's the JS-2 unit. It'll misfire after a dozen or so firings if the battery is low, then it'll be alright for a while. I contacted Tamiya and they'd take it back for service, but I haven't sent it in yet.

So yes, you should be able to isolate the trigger coil and supply a separate cap feed from the battery to make an auxiliary flash unit. Just keep in mind that's a lot of voltage, I think I read it's the same type in those portable defribrillators.