Of course you can't repair a Tizzie without a Corsair who knows about them. Funny thing is, I'd bet there is a Corsair out there who is willing to do the work for the Reavers for the right amount of cash. I mean, it isn't out of the realm of possibilities that a Corsair leaves the Empire for another walk of life now is it?
The Elders made a decision and then inaction caused the Reavers to turn on them. Being shot with your own weapons are the consequences of said actions/inaction. You'll notice the Reavers aren't docking with Corsair bases, that is a consequence of their action of turning on the Corsairs and shooting them.
As for the free use? The tech permission said free usage and I'm sure they were stocked up before the Reavers turned on the Corsairs. I think I have one fighter with Corsair kit, my two recent builds use other technologies. If you don't want unlimited use, limit their use in the permission. Fairly simple.
If you don't want to get shot by your own guns you have two options. Don't give them to a mercenary or ensure you keep the mercenary you did give the guns to on your payroll. Extremely simple.
I don't hear the GMG complaining about getting shot by their own guns ever. You lie to them in role play to get them? Instead of whining on the forums out of role play. They just file a bounty on you if they ever find out you broke the agreement you made with them.