If it's super risty you may want to make sure you've got enough cash for a new pistol assembly... not expensize but certainly something to be aware of should you twist off the bleeder nut.
While your back there, pull back the boots where the pistons come out of the bore, and check for fluid leaking/seeping out. (fig A) If you see any, that's bad, and I'd suppose could cause low pressure on that circuit as well.
fig A
