All the above is good advice and I am going to chime in unusual for me to give advice but I had the same issue and it seemed no matter what I did I could not get away from it.
One night I was practicing and one of the youth coaches came over and ask me if I had arm pain after I was done bowling I replied no and believe it or not I know I bend my arm but it feels totally relaxed.
He said that was good but he noticed my balance arm was all over the place and he believed that was what was causing my swing arm to bend, my balance arm was causing me to have tension in my swing arm because sub consciously it knew it had to help keep me balanced. he suggested that I keep my balance arm pointed down lane through my approach and letting my swing arm naturally force to the out position at release, bingo no more bent swing arm.
Now I am not sure if that was a bunch of whoie just to get my mind of my swing arm or what but it did work for me and if I don't point my balance arm down lane my swing arm will bend so it seems to work for me anyway.
Again just my 2 cents take it for what it worth.
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