Hydraulic Issue

First, I would contact the people who replaced the hydraulic oil and find out what they really put in there.  Sounds to me that they should have the responsibility to fix it.  I would not run it until you know what they did.

RonJ

The foaming means the pump is sucking part oil, part air.  Sounds like it is very low on hyd oil or it is sucking air from a loose fitting.  You will have to let is sit for a while before you can check it as the foam has to settle.  As Ron suggested I would get a hold of the folks who changed it.