I have had two personal experiences, here. One boat that I own I found a leak on top of the tank where rust occurred due to water infiltration from above. I cleaned all the rust off and got the top of the 175 gal tank back down to metal. When I was done, along with many, many pinholes, I had a whole the size of a golf ball and one the size of a soft ball. I decided to glass over the entire top. I built up multiple layers of mat an woven to about a quarter inch. That cured the problem and it is going on 3 yrs. The "right" solution would have been to remove engine and install a new tank and while at it, do the other saddle tank at a price of around $10,000. After all, the boat is 30 years old with the original tanks. That job will happen, but it would be more practical if I am ready to repower or to do a complete overhaul on the engine. Another suggestion is to cut tanks out and replace with smaller tanks and try to forgo removing the engine. On another boat that I owned a few years back, it also had developed a leak in the fuel tank. On that boat, I stripped the engine down and could actually slide the tank out. I brought the tank to a welder who suggested welding a new bottom on. I did that (for $320.00). I re-installed the tank. The following season it started leaking again. I had to replace the entire tank. What a pain! What I learned... If the leak is on the top, you can get away with a patch. There are multiple opinions on fixes. If the leak is on the side or bottom, forget it. Imagine you do all the work and it still leaks. If you are removing engines, yes, do both tanks. If my tank(s) on my Albin develop another leak, I think I will cut them up, remove and try to fit in smaller tanks. Those friggin Lehman's are heavy! Thankfully, I only have one. Good luck. Bob