Following on from John's comment, my M15 did 2hrs at 4m in QAB marina and still works fine, hence the string coment and tie it on!
We regualy add silicon (not vasaline as it rots rubber seals
) grease to the shafts to stop salt build up and water working its way through due to barometric changes. The M1euro escpecailly needs some silcon worked down between the squech and volume knobs, to stop salt binding the knobs.
Rgds
James