Marx #21 Diesel

While doing routine maintenance on my Marx 21 locos I noticed that one has what appears to be a weight attached to the brace between the trucks while the other has a brace but no weight. These are both powered units. I am puzzled why Marx would put additional weight in a hefty locomotive or could it be that a former owner put it there (these were bought through ebay but from different sellers). Anyone have any thoughts on this?

I have 2 powered #21s without weights. so it was probably added after. but in the toy train world; who knows for sure.

Any more Marx 21 owners want to weigh in on this? I was under the impression that these locos were pretty common but, judging from the paltry response to my question, I guess they aren’t.