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The centre "tank" appears to be tapered on the green repainted model, but larger end (ejector ring?) on the orange ones. I am hoping to try brake fluid on the green one as it looks like it was mint before it was painted and came in its original box.

I think, the resizing of the ejetor rings is typical for all models. Sometimes is changed only the height, sometimes diameter and sometimes there are added some rings more. Usually the very early models have a small and low ejector ring and the late models have higher ejector. This topic has been discussed e.g. by the 13d Dodge Wreck Truck. It is a question, from point starts the resizing of the ejector ring the real variation.
Antonin
The early reverse Wreck Truck with low ejector ring

The late superfast Wreck Truck with high ejector ring

Hahaha Antonin you show off