I believe it is the filter you mention. I was wondering if they changed the filter and neglected to put that in.Does that unit have the 3 pc filter set-up with the long bolt holding it all together.??
Check that top oring.. MAKE SURE it’s UP IN the filter head..
Someone else mentioned the “OLIVES” in the inlet and return.. they’re also in the filter head end.. don’t overlook them..
How about the filter under the inlet nut..
To check it, remove the inlet nut, remove the big spring..
HOLD THE GUTS DOWN WITH A POCKET SCREWDRIVER.. and with a 90* pick, dig out the plastic filter..
Hope this helps.