Bear in mind any heating or welding of aluminium softens it and it won’t return back to its full strength without artificial ageing or quenching depending on the alloy.
Hah, timely this, been making a new gearbox backplate for my ml7 - I bought it semi refurbished, with a broken backplate, repaired end cover, worn bushes in the layshaft (is that what its called?). Anyway, the layshaft has some serious wear in the bronze bushes, I considered making some, bet maybe easier just to buy them?
Toying with selling it tbh, I've had it 10 years plus and never used it, except when I used the Amolco milling head to drill the idle mixture screw thread out on one of my mikunis the other day.