Do you have the plastic or bronze housing and if plastic, are any of the stator vanes cracked or missing? I can see the potential of a plastic housing flexing, possibly, and causing the phenomenon you're experiencing.
Of course, this is only a possibility, but I happen to think you're on the right track. It could also be some sort of issue with your transom flexing under load, I suppose..... and any of the various ideas expressed above.
ive been looking into new housings it is all i can see that is left.. do the housings get shimmed in anyway,, are the replacement housings stronger than originals
another season coming up and i want to be ready
thanks in advance any input is appreciated