The larger o-ring at the right is between the dist. cap and distributor housing. Yours is cracked and shrunk, it’ll let in moisture and dust.
Distributor shaft o-ring
Fits on the dist. shaft into your cylinder head. Can be the culprit for oil leaks on the drivers side front of your engine. Yours is hard as a rock. Replace it with the proper o-ring and don’t worry about it again. (included with our full gasket set)