David,
On all pictures I have seen of Avalon at the museum the right hand track is missing. I presume the track was left in the field where Avalon was knocked out and presumably "borrowed" as spare for another Sherman, or even as armor which seems to be quite common in late 1944/45.
I visited "Broekhuizen" a couple of months ago, and searched for the field where Avalon supposedly was put out of action. It's to the Southwest of Broekhuizen. As you will see from the pictures there isn't much more to see than just a field, but the trees in the background hide the ruines of the Broekhuizen castle, that was in fact destroyed during the battle in 1944.
