Back in the mid 90s I had two 400K mechanisms still new in the beautifully folded anti-static bags from Apple.

Both drives were locked up tight. The mechanisms would not move when one attempted to insert a disk. The "lubricant" applied at the factory really hardens up after the VOCs evaporate.

All that was required was to clean the sliding metal parts, easily accessible on the sides of the drive. No disassembly required. And then relubricate.

Of course, your drives may have a different problem, but the method that worked for me is non-destructive, low risk and a good place to start.