Main gear down lock checks
 

Only gear problem I ever had was loose nut on right main gear down lock switch came loose and wouldn't allow completion of down cycle. The gear was down and locked, but doors couldn't close, and hyd pump kept trying - the hyd pump was wipped out.
In my parts manuel -65-68 - pic of main gear down lock shows mounting nut and a horse shoe shaped bracket, the nut came loose and that bracket dropped out. sw dropped out of place.
The only damage was hyd pump and new skivvies.