So right now I have a WC setup using 1/2" tubing on a Lanig D5 pump and PA 120.3 rad. I want to use smaller tubing this time around, as the larger tubing was a wee-bit too big. My problem is that I am unsure as to what size tubing I can use with the parts I have. I know that I lost any extra parts or fittings that came with the PA rad when I moved. Are there extra fittings I need to replace to downgrade to - say - 3/8 OD tubing?