Rust under a fillit weld,sounds like cold lap,on one of those mig welds that every one is crazy about,if you have a weld failing on something as simple to weld as a small tractor loader,it is indeed the welds fault,welds shouldn't fail first,,the material should,,maybe the weld didn't fail first,and cause this,,can't tell from pictures,,but if you got rust under a weld leg than it is either cracked or not fused to base metal,and its been that way for a while,,you can get a lot of lack of fusion with short circuiting mig,if not done right,,,can't tell what it was welded with,,flux core and stick are less prone to have these types problems. Ask the guy who is going to fix it for you about this,,,if it was the welds failing that caused this,,there could be a case against loader seller/manufactor,,despite what all the other people have been saying.
There are ways to check for cracks on the other welds,,,but unless you have the stuff than that probably won't happen,dye penatrant,is a good way,,,,you can clean the welds of paint and look real good,,maybe with a magnifyer,,,look real close at the edges of the welds where they tie into[or not],base metal,,,thingy