Most Bosch solenoid caps are crimped on. You will need to be able to buy a new solenoid since opening it and renewing the contacts requires tools you will not have.. Next is brushes. Permanent magnet starters the entire brush assy. is replaced. you will need to find that part. Wound field starters, the brushes are usually spot welded. . Next is the drive. The equipment to open, replace springs, clean and reassemble a crimped drive is expensive, so you will need to buy a new drive. Unless you have the ability to buy wholesale. those parts will cost more than a reman starter.
Some starters have a failure point, like NipponDenso contacts, but you said Bosch Old delco starters are easy to renew, they were easy to disassemble, cap and brushes screw on, drives usually very robust and can be reused.
Sadly, those days are gone.