Years ago when rebiulding my first GPA I addressed the problem of wheel cylinders that seize up when placed in water.
I manufactured bronze pistons and sleeved the wheel cylinders in stainless steel. 15 years on it is still using the same cylinders and pistons with out an over haul. Sure beats changing them every year.
I soon discovered that in Europe and America you can not get the wheel cylinders sleeved.
I have now purchased about 5 sets of new wheel cylinders sleeved them all in stainless steel and made bronze pistons.
These sell for $566.00US for a full set. Not cheap but you only need to buy them once. Unlike the conventional ones that donot last.
Let me know if you would like a set.
Best regards Richard