New guy with slipping clutch

Hi guys - I'm new to the board and unfortunately found the board because of a problem keeping my car off the road.

My daily driver is a 72 scamp with a 225 3-speed, A904 transmission. See picture below of a camping trip I took with my daughter. Dig the carseat in the back. Yes, this is my family car!

I've recently and suddenly experienced major slippage in all gears.

Can you guys give me some ideas of what to look for under the inspection plate to properly diagnose the problem? I know metal shavings, oil, or grease would be problems, but what degree of wear on the disc is acceptable? Will a disc that is worn too far be obvious on sight or are there some sort of wear indicators? I am willing to replace the clutch if necessary, but want to verify that it actually is necessary before doing so.

I replaced a clutch years ago in a Chevy truck so I'm not entirely unexperienced in this area, but again just want to make sure clutch replacement is truly necessary before I take the plunge.

THANKS for any tips! :notworth:
Andy