I bought the same Jagdpanther display kit last year, thinking that if prices were high then, in the future (post -the currently mythic Brexit) they'd be somewhere out in the Cosmos.
The AAF museum is an excellent Tamiya parts resource for but, even if you can persuade them to ship at a budget rate (default rate can cost more than some significant parts ordered

), it can still be
very pricey.
I often buy from Axel but he, in turn, gets most (if not all) his spares from Tamiya's European HQ. Formerly, that was Dickie-Tamiya. Now they're restyled 'Tamiya-Carson'. Shipping from Europe means, for the present anyway,
VAT is already paid, and shipping rates are well below those of the US. Shipping from the US may also incur additional Customs charges. (Depending on the product and its value.)
All of that said, I've never bought from Tamiya-Carson direct, so their spares dept. is an unknown factor to me.
https://www.tamiya.de/en/products/rc-mo ... tanks/I've never tried Tamiya's UK rep.,
Tamiya's default UK outlet is the Hobbyco. Again, I've never dealt with them, but I find their website slow and clunky. I don't know about you lot, but that can be off putting.
http://www.hobbyco.net/scripts/oe11.3/c ... gkabMcjgckSee what i mean..
As for the gear repair kit, as far as I'm able to tell, the innards (gears and shafts) are probably the same for most full-option models. I'd guess only the frame, output shafts, and standoff positions differ from one another.
I have a brace of old Sherman gearboxes, and I'm going to try to transplant them into the gear frames supplied with the kit. There's no harm in trying, eh?
Adam, (Ad Lav) is probably our Tamiya professor. I'm sure he'll know what possible options there are.

Where are you, Adam?
