I have an open loop 2-zone radiant heat system (built ~2005, mix of pex, brass & copper) and I have 2 problems:

1) The gaskets in my (brass) manifolds are leaking. Evidently these brand manifolds are renowned for their cheap gaskets (aftermarket fixes are available)
2) One of the loops in a zone has a towel heater. Evidently if this loop is turned on @ the manifold I can expect very fast corrosion.

Questions:
- Are small heat exchangers + pumps sold for these kinds of towel racks?
- What is the recommended procedure for replacing the gaskets (i.e. draining the loops off the manifold)? There is a shutoff valve to the manifold but I'm wondering about all the water in the loops off the manifold.