Yes, Titanmike I've seen and digested the method. This new to me trailer was used as a fishing cabin on the Texas coast and probable spent most of its time on city water. I pulled the pump and opened up the head and everything looked really clean so it was reassembled and pumps fine. It didn't take long before it leaked. Spent several times going through the steps and one time it went about 5 days before the tank showed full and overflowed out the belly pan.
Thinking it may have been a ruptured tank caused me to check both grey and black tanks (massive cleaning of the black one) before proving it was only the pump. February 2021 was a bad cold spell in Texas so I was afraid of almost anything being wrong. As I'm a 74 years old recent widower, I have no help and being 6 foot one inch doesn't allow for working well in small places.
The cost of a new pump is not the problem. I don't want to make a continual habit of playing with a pump with brittle parts that aren't going to stay working. I've read that even new pumps will leak so I've raised the by-pass setting 1/4 turn and just lowered my adjustable pressure regulator (not an off the shelf unit) to about 40 pounds (the two gauges don't agree) before this test.
The original question still stands concerning the 4048 asking if it's possibly a newer head design with an improved by-pass. That is not mentioned on the Pentair website hence the question.
2009 Duramax w/Transfer Flow Fuel Tank
2017 Rockwood Windjammer 3029
Almost South of the Border