I never experienced a catastrophic leak, luckily. Most of our exercises simulated water for fuel, especially in the large bladders/blivets. In my condition last night (sick, not drunk) I should state there is a difference between bladders and blivets. Blivets are usually less than 3000 gal and are designed to be rolled and moved around. The most common blivets are the 100, 250, and 500 gallon ones. The bladders are made to be positioned in a prepared pit and usually start out at 3000 and go up to the largest one I saw was 300K.
A few years ago I did general inspections of these type items and for the most part, I found the 3K and above stuff had been sitting on the shelves for well past their expiration date. Some were very obviously disintegrating and these were most usually the bladders at 3K and above. Many of these were so stiff they could not be opened up without cracking the rubber. Most, if not all of these were made during the ramp up for desert storm and had sat ever since.
The blivets usually faired better. Out of about 100, I ran into only 3 that I would not have felt comfortable using. They also get stiff and can crack but the ones I saw had either been used more frequently, were later manufacture, or just maintained better.
Repairs, technically yes. Effective, yes if you have all the right stuff and the hole is small. Weather cracks, forget it. Seams, good luck.