Marvel Mystery Oil

How much Marvel Mystery Oil to add to the crankcase in a C-85-12F engine?   My mechanic suggested using some to help with oil consumption which is now at about 1 Quart every 2.5 hours.  High time engine but seems to be running strong.  Any recommendations would help.  I used MMO in several of my Bonanzas over the years but can't for the life of me remember how much I added to the oil.  My memory of these incidental things has gone south since I turned 83 this month!!  

As a side query, I wonder how many ERcoupe pilots are in the eighties and still flying their Coupes.  Just curious. Thanks in advance for any and all responses. "Keep the blue side up!"