Replace it!
I bought my '79 H30 Cherubini this past July. The fuel tank was replaced prior to my making the purchase with a plastic Tempo 11.5 gal. (#640020), or 15.75 (#640054). It should go without saying, I was delighted that I didn't have that expense and headache in front of me. I cannot stress enough that my opinion is replace the aluminum with a new plastic. I base this on my inspection of the metal fresh water tank which is really showing its age.Measure the space before you buy. The survey on my H30 said I have 15 gal., but it looks smaller. I need to make measurements to be certain since I cannot read the manufacturer's tag. However, this is not a major concern. With the Yanmar YSM12, I get 20 hours of motoring. Nonetheless, I carry at least one five gal. jerry can even on overnighters. The Tempo tanks are fitted with 1 1/2" fill, 1/4" pickup and 5/8 vent. A sending unit is included. It appears that the old tank was removed and the new installed through the engine access hatch (the companionway steps) and over the engine. The bulkhead in the lazzarette was removed to facilitate installation of hold downs and hoses. You should make all wiring connections for the sending unit at installation. I am not trying to sell Tempo. That's whats on my boat which should be about the same. Regardless, there is nothing worse than a leaky fuel tank except maybe a leaky holding tank. Replace it now.