Odd leaking valve problem

[kernal]

Installed a Brand Hydraulics compact valve on my 2320 to run the snowblower rotation and chute last Dec. Everything works great, except it leaks from the spool's, not the connections. The odd thing is it does not leak while the tractor is running. It only seems to leak when it's sitting overnight, etc. Called Surplus Center, have and RMA number, just trying to think of anything else I should check before sending it in.

Any idea's?