I recently installed these aluminum seat strap buckles. They are a direct replacement for the factory plastic buckles.
The swiveling part of the plastic buckles broke years ago, and I just tied the straps onto the remaining part, which is much beefier and held up fine, although it is now visibly bent. On new boats I automatically remove the swivel and never give it a chance to break.
But this loses the easy adjustability of the original buckle, and I think it is just a matter of time before the remaining plastic part breaks as well. The aluminum buckles restore that adjustability, and are much stronger and I don't worry about them at all. And they look great.
I found these on eBay while looking for replacement buckles to carry as spares. They are not that much more expensive than the plastic ones. I tied the old buckles inside the 'trunk' just in case.