Gas tank leak repair

Good evening all,

I bought a 1996 RMW in late August, number two.
The gas tank has two hair line cracks on the top of the tank in the depressions above the tank strap attachments, front right, rear left.
As there aren't tanks readily available, I am going to have a friend weld the two cracks.

My question is the composition of the plastic.
Are the tanks Polyethylene?
I plan to purchase filler for polyethylene tomorrow at Graingers.
Their product HDPE 5/32"
Has anyone ventured down this path successfully?
If not, I am about to find out!

So my main purpose at the moment is to confirm if the tank material is polyethylene.

Thanks for any advice,

Bill

According to the FSM it is HDPE High Density Polyethylene.

There is someone parting out wagons on the west coast. He has advertised in the parts for sale section. He may have a tank or two.

https://gmlongroof.4umer.com/t9886-the-roadmaster-farm-parting-out-6-buick-wagons-1-1991-2-1993-s-2-1996-more-parts-from-previous-parting-outs

Most sources recommend against field repair of HDPE fuel tanks. Small leaks might indicate a general degradation or manufacturing flaw that is just now showing up. Used ones are available, this might be one source: http://www.onecallfueltanks.com/Order3.html

Good Luck on whatever route you choose.

Thanks to your replies, a link from Fred led me to a "Buicknutt" in California for a fuel tank.
I will still have the cracks welded in the original tank to check the feasibility of welding polyethylene.

It's great to be able to access a resource with a wealth of information.