Perry 951

If that is all you want to replace, you can do that. The other gasket that is sandwiched between the block and the housing also has an o-ring that surrounds the area where the valve is. If that is blown or nicked, it can cause mixing as well.

Your call.. but I would do it all just to be sure... since you did not do it before.

What you can do is remove the valve and check the seals. If they have problems, then you could be Ok on the other gasket.