All of the TnA trains can be somewhat difficult to repair. I bring up the other ones because I have expierencied different issues with different ones. This is an attempt to give you an idea on what you "could" be in for. Not knowing anymore info on the D10 that you are looking at it is hard to say how difficult it would be to repair it. Does the person selling it specially mention it doesn't work or say what happens when the try to make it work?
Regarding the battery terminals, if you can find "new" replacement ones I would be indebted to you..😃. Seriously, I have looked high and low, far and wide for these things. From the US, UK, and finally finding some on one site in China. As far as being in trains, they may not be uncommon, and I have stripped them from a few different models to use in TnA repairs but would love to just have brand new ones to use.
Replacing D10's cab should not be too bad, but are you talking about taking it off and then putting the same one back on or actually finding a replacement cab. The only difficult part which is not too bad on this model is getting the wires tucked back in.
Hope this all helps...😃