I have a 98 ZL440 and They made a 99 model.Are you sure it is not a ZL 500? I don't think they made a Zl 440 in 1999. In 99, I think the only 440 liquid they made was the snopro.... but at any rate, I have a Zr 500... which is very similar to the ZL 500 (assuming you have a 500 and not a 400.)
I do not know of any problems or concerns with that model. I absolutely love my Zr 500. The Zl is basically the same except the suspension is a little different, and you get electric start, and maybe reverse.
I think you will love your Zl. I have 4500 miles on my Zr and last week was the first time it has gone to the shop. Needs new slide rails (I am doing them)... but also needs some engine work and since it is an EFI, I don't do any of the work on it.
Have fun... and you better tell your wife how much you love her right before you book for the door to go riding.