that's the isseu with the cheapest tanks like Heng Long, Matorro and WSN you get what you pay for, although the latest HL are pretty good but still miles away from the quality of the tamiya stuff, that's a proven fact, no doubt about that.
Everything is repareble, the one links the other, cheap means: little of no quality controls, cheap commodities not very well thought on planning etc ment more like a toy tank

Its just like with beautiful women , some have no haert ... others are angels ... these tanks are the same some are running, others have little isseu's ... yeah you can repair them ... but upgrading is expensive you will end up at the hights of the tamiya prices ... better electronics Elmod? Yes but better priced then tamiya the elmod will cost easy 400 to 500€ the tamiya MFmodules around 160€

The heng longs have the cheapest mf RX18 with sherman like motorsound ... compare but choose quality you never regret that descision ... no spare tanks for parts with the tamiya stuff at a very concurrental price : the KT, Tiger I, Sherman 400€ Full Function

Compare HL and Matorro with crapsounds 100 to 200€ much cheaper but that's all said