No, acrylic is fine sitting for a long time, nothing to dry up or crack like silicone. That's actually why I went with acrylic for my 240, my 265 was a pain and leaked after I set that glass monster up so I made a promise to myself that any tank I get that is over 125g will only be acrylic. Just have him send you pics of all sides and corners and look for any crazing in the panels and corners. Long as you don't see that then you should be good. Ask him how thick the panels are as well, you will get some bow in a tall acrylic if the panels are not 3/4" or better. It's not a deal breaker by any means, my 30" tall 240 is 1/2" and bows about 1" without any issues, but thicker is always better though.
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