The whole idea about Deca 'lubing the joints' -- is irrelevant in this case (yes deca does help the joints,, but..) because "tendons" are not joints and Deca will not do anything for your actual tendons or tendonitis.
Deca has helped achy joints, but only thing that ever helped my tendonitis,, UNFORTUNATELY was taking a lot of rest and time away from the gym and then lifting extremely light when coming back.
if its bad in your elbows,, don't do any pressing exercises for a month, just take the time and work on your legs and cardio and give the elbows time to heal,, you'll come back with stronger legs and better feeling elbows.