Ours did the same thing a few years ago. I can't remember where I found replacements, may have been on Ebay. Part of our problem was that the originals were screwed to the cabinet frames too close to the back edge and the wood started to split and allowed the struts to move. I glued small pieces of wood in the original holes and when I installed the new strut I moved the mounting position up about 3/16" to add extra pressure when holding the door up. Works good now. I mounted one and made sure I didn't make it too tight before I mounted the other three. It helps to have a helper to hold the door up when your changing these. Good luck.
Thanks for the replies. I fabricated a piece of wood to hold the doors open when loading and unloading the cabinets. They will work well for helping replace the struts. The longer that I own the motor home the less I like Thor and the more doubtful I am that it will hold together for long. What a POS.