How to fix the scanner handles

It will most likely require an entire scanner assembly, unless Samsung has the service parts available as a separate component :-(. The problem here is once you replace the scanner, the replacement scanner module will have different calibration data which needs to be matched, so you will need to have the reference calibration sheet and the tools to adjust it as it almost certainly isn't in the onboard tech mode diagnostics on the more basic printers but YMMV. Even if it was, you need the Samsung reference sheet which likely isn't available.

What makes it worse for you is that this is a pre-HP Samsung. HP didn't exactly give you guys much of a break for spare parts availability—they put the engine in the cheap laser printers, released a few color lasers with the Samsung color engine, and released a few 11x17 color lasers using the Samsung 11x17 commercial engine. Almost all of the older models had their supply line cut short shortly after the buyout outside of the ML- engines they still run in the cheap HPs today.

Your best bet to fix this is to buy a scanner assembly for the higes and transplant them to yours - don't do a complete assembly swap, as you cannot properly scan files until you go back in and calibrate the new scanner head module. That said, this will not be cheap, so if you can get them from a dead donor printer (preferably free or next to it), that will be the most economical way to get the part.