Just because the plunger could be removed the way you did it doesn't mean that you removed it in the proper sequence - or more important, that you replaced it in the correct sequence. I.e., it might not be step 20 of a 20-step procedure. It might be step 4.

I think it is time to do a complete teardown and find out what happened. There are photos if you search that show o-rings that seal around the six ports, and they may have become dislodged or damaged by removing the plunger. They appear to install with the entire assembly apart.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7