Pretty hard to get a GT 40 water tight, it has some holes to fill. lol
I put 3,500 miles on my SPF GT40, and I learned a lot in those miles. I think the best advice I could give if you really want a trouble free car, is to take the car apart and rebuild it. You don't have to take the entire car apart, but I would rebuild all the suspension, shim the wheel bearings, install better shocks and springs, swap out all the switches, lights, gauges, and fuel senders.
My GT was built when there was supply chain issues, so maybe I did not get the typical spec parts. But I replaced several switches, gauges, lights, and fuel senders.