You wrote:
</font><font color="blue" class="small">( If the robin engine filter is the same as the older ONAN's (opposed twin) then you can use the motorcraft FL-400S, Fram TG3600 or Purilator Pure One 20195. I have found these filter to be much better than stock Onan. They have three times the filtration area and finer filtration. )</font>
For owners of PT425 with the steel tank (Kohler engine) these would be the correct filters also, BUT they are too long with the engine as it is installed in my PT. Didn't feel like pulling the motor (the filter would fit, but can't be removed or replaced) or cutting a hole in the side, so I found the equivalent alternative shorter ones. Will post that number when I replace the filter next.
Mark H.