Reseal or not? 9 years old glass 55G

I have a couple of used 75's that are 19-20 years old. Both were stored dey for a few years, but hold water w/out any problems now. They don't even have center braces; the glass on the older tanks is thick enough not to need them.
 
I got my 55 on craigs list and he said it had no leaks... but it did... resealing it was surprisingly easy :-)
 
I have an old 55 gallon with a slate bottom that still doesnt leak with original seals.its gotta be old..the glass has a green tint no matter how clean i get it though..Its my feeder convict breeder tank
 
A little off topic, but does anyone have instruction about how to reseal properly, I think I might have to soon and need to know how.
 
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