Hi frodo,
Since you didn't say anything about bailing water out of the area, I assume it's a slow leak.
If it happens all the time, whether running the washing machine or not, I would say it's probably the faucets, hoses connected to the faucets, or the fittings where the hose attaches to the washing machine. If you can reach in from the closet with tissue paper, you may be able to find the leak by pressing the paper against the various connections.
If it only leaks when using the washing machine, there are some parts inside the washing machine that can crack if the washing machine was not properly winterized. Even in central Florida, it's possible to go below freezing. And as at least one person here has found, if you set the machine on the wrong cycle when winterizing, not all parts inside get properly winterized.