When I bought my 1979 Sovereign the Zip Dee awning arms were stuck and would not move. The fabric was fine but the arm just would not extend. This is how I fixed it. It was probably better to buy the correct parts and replace them but I was short on cash after the purchase.
First remove the awning arms and take a skill saw with a carbide blade and set the depth at 1/8 of an inch. Wear safety shield and goggles and saw like the picture approx 1/8 from both edges.
After the cut you can pry the aluminum open and remove the stainless steel arm. Mine had white corrosion powder caused my a reaction where aluminum and stainless are left together for a long period.
The old arm after removing the stainless
Mark new tubing. I got mine from Amazon.com. Make sure holes are perfect.