Bydlo,
"The big unknown is it's matching with 3012R...possibly problematic due to loose bearings, but maybe FD-200 damper will help."
Maybe not. If the 3012 has loose bearings, you're ill advised to use it at all and especially with a Decca. A band-aid won't help much. Fix the arm first. You'll be tearing up your records with that arm/cart.
"The big unknown is it's matching with 3012R...possibly problematic due to loose bearings, but maybe FD-200 damper will help."
Maybe not. If the 3012 has loose bearings, you're ill advised to use it at all and especially with a Decca. A band-aid won't help much. Fix the arm first. You'll be tearing up your records with that arm/cart.