Did you receive any answers to your question? I have a 41 and have replaced all of the tanks and wired for guages. The fuel tanks are located under the Salon sole to each side of the center battery well. The factory tanks are aluminum and if have not been replaced are likely to have corroded to the point of leakage at the corners where water would have accumulated, or are near the point of corroding completely through. I would have a tank leak test done before getting too far from a facility that has the ability to cut the fiberglass covering the tanks and then re-glassing and painting. The original Irwin configuration did not include tank quantity guages.
Bill Fowler

Irwin 41 - Lying Highport Marina, Lake Texoma, Texas
bill@ffmria.com