Have those pesky tip guides giving you no help? Do you find this game boring after slowly derusting every part? Well ill show you how to make that go away:

(You must have atleast 10k or more so this can work!)
1. go over to the tank and buy all missing parts.
2. then dissasemble EVERYTHING, do not derust any of the parts!!!
3. find the parts menu, click select all and click the restore button. (restore it to the painted condition)
4. Assemble the tank and dont forget to derust the hull, turret and the "engine"
5. finish the contract (and if you have all the upgrades for store and missions, this can range from 60k to 100k)