the tank is mounted on plywood and strapped down. We replaced mine about 3 yrs ago now. the whole tank came out the lazerette with the filler neck cut off. I don't know if your boat is exactly the same but it's not a terribly difficult job. replace the fuel lines, filters, and make very sure you get clean new fuel when you fill the new one. I used a Moeller 19 gal that I can now remove in about 20 mins if necessary.Have decided to proceed with purchase. Got reduced price to compensate for diesel leak issue. should close sale soon and will start looking for leak and fixing other issues.
by the way, the leaks in the tank are most likely in the bottom and slowly leaking into the plywood support. really tiny pin holes make the bottom of the tank porous, don't think you will find actual holes like most people think of.