Welding a 5052-0 Fuel Tank

Anybody got any pointers on this. A friend had an aluminum tank
welded and it leaked. He thinks it was because a different aluminum
was used for the welding rod. I dunno. I'm a novice on welding.

This tank has a big dent on top and we may need to drill a hole or two
from the bottom of the pancake-shaped tank to work the dent out. Will
this 5052-0 aluminum get hard and brittle? It's .040 thick. The dent
needs to be worked out because we need an airfoil shape on the top of
the tank, and we lost the desired shape with the big dent which made
the tank's top bulge around the inlet. It's an 18-gallon wing tank.

Thank you for your kind support.

Yes, thanks and I'm kinda enjoying (but a tiny bit ashamed because
schadenfreude is a sin) watching the group of ravenous piranhas
picking the bones of Jim Campbell, as if he deserves anything better.
Poor guy. He just can't help himself. He's innately evil. Besides
being an irrepressible narcissist. And I think he fibs sometimes too.
And tells cock-and-bull stories. I got a feeling Ron Wanntaja has
Campbell assessed correctly. His credibility is shot. So I tend to
believe Wanttaja, who more often than not demonstrates sterling
character. Or at least better than average character.

Ok, help us out a little now with this welding thing.