Replace it! Urine is so corrosive that it can eat through any metal tank, even 316 SS. The first leak (which is always just the FIRST leak) is usually at a weld--a seam or fitting, typically within 5 years while it's gradually turning the bottom of the tank into a colander.
Ronco Plastics
Ronco Plastics marine Tanks is your best source for a tank. They make TOP quality thick-walled water and waste tanks for a very reasonable price and have more than 400 shapes and sizes, over 100 of which are non-rectangular, and they install fittings in the sizes and locations specified by the customer when they make the tank. There are retailers who sell Ronco tanks, but Ronco sells direct for a much lower price...and they're great to work with.
When looking at drawings it's important to know that there is no top or bottom until the fittings go in, and YOU decide where they go. So rotate, flip in any orientation to find the tank that fit your space. The v-berth is a great location for a waste tank, btw....provided the toilet isn't all the way at the other end of the cabin.
I'll be glad to help you select a tank, specify the fittings locations and work out plumbing runs that will give you a simple-to-use and maintain trouble-free and odor free system. Send me a PM if you want my help.
--Peggie