Well I'm no doctor.. But I'm suffering from tendonitis as well..

I think i developed my tendonitis in the elbow [left] from training in cold weather, training explosively and locking out weight.. Me personally, I never stopped training with it.
I still have it. But I've been taking a Glucosamine,Chronodrin,MSM triple strength supplement and I feel its helped me tremendously.. [my knees too]
Again personally i've never used Deca yet but all the joint comforting effects sound promising.