That's The Way The Plastic Crumbles...

 One of the locomotives I have a real soft spot for is the Marx battery powered 0-4-0. It is a cantankerous beast, yet looks so much like what one would imagine early American made H0 might have looked like if, say, companies like Marx or American Flyer (pre-Gilbert!) had gotten into it earlier. In fact, it is very similar to the Trix Twin 00 scale/H0 gauge "American" 0-4-0 from 1938.

(From the TCA Western Trix page)

By itself, I think it resembles any number of locomotives from the Pennsylvania Railroad, what with its somewhat Belpaire-esque firebox, as witnessed by my conversion of one into an ersatz E6 Atlantic.

I had another one arrive, specifically to have spares, but decided to try and resurrect the little beast.

Things went wrong rapidly. 

It arrived on the heels of some more parts for a planned PRR H8 conversion from a Tyco "Chattanooga Choo Choo" Consolidation. Again, I found myself thinking of how similar the Marx boiler was to the Trix and Pennsylvania Railroad designs, and wondering how easy it would be to simply use those parts. But now I had this new "parts" Marx arrive, so naturally I decided to restore it. To that end, I carefully removed the chassis and wheels. That spare Marx "Green Valley" boiler was the one planned for another project.

Sadly, this was the end result.

Aside from the boiler, all the chassis plastic was remarkably brittle. It crumbled, right down to the gears. I've never seen a hard plastic disintegrate like this. 

In the end, the intact boiler will be used to replace one that is not quite in the best shape on another of my Marx models. However, the Green Valley unit boiler is now facing a future as the one for the Pennsylvania H8 Consolidation project. It's just too close. That, however, is for another time, as I have other projects in queue.