Does anyone know what plastic the OEM saddle bags are made from?

I believe they are polypropylene.

Dan

The plastic seems very hard not like dirt bike pp.  Could it be glass filled or some thing else?

I repaired a crack where the bag hooks to the antler.  Can't remember but thinking it was a few inches long.

I did not see any evidence of fiber content in the plastic.

I took a piece of paper and cut a pattern to match the area I wanted to repair.
Transferred that pattern to aluminum sheet and cut out a piece to match.
Did the same pattern making/aluminum cutting for outside of bag (it was a simpler shape)

I formed the aluminum to match the contours on the inside and I believe the outside pieces were just flat.
I drilled rivet holes in a number of spots.

I put black rtv on the backside of the alum pieces to seal out any water entry and riveted into place using aluminum rivets.  Has held fine since the 90's.

I also painted the outside of the alum flat black.  Don't recall if I did before or after install but can barely see it when bags are mounted.

Best way to repair bags is plastic weld. Few if any glues are strong enough.
If cracked, (after plastic weld), install a piece of metal inside the bag and attach it. 
Seal from inside with whatever.

Ride safe, Ted

This is kind of funny.  I went to put the one good bag on and the bag that is cracked is not from the side the bike fell on.  It is from the non fall side.  It must have been cracked the 4 or 5 years I have owned the bike.  The cracks are small and can only be seen when flexing the mounting area out.

The plastic seems very hard not like dirt bike pp.  Could it be glass filled or some thing else?

It's not reinforced but there are dozens of grades of polypropylene.

Dan

I went to a guy who welds plastic bumpers.  He was referred by a buddy of mine who was an insurance adjuster, said the guy does good work.  He welded my bag and it looked good.  I noticed after a month the weld wasn't holding so I was picking at it and the whole weld came off and the plastic looked the same other than where he had melted it a little with the welder.

Plastic welding is not always a particularly deep weld...
Can/will break again if in a bad location. On the bags, reinforcement is needed.
Ted

Read the Bodywork FAQ for info and helpful links:
http://www.zggtr.org/index.php?topic=659.0