Had you ever seen the tank leak before, or are you just assuming that “it must have leaked” because there was water around the base some time ago? The reason I ask is that you may not be dealing with a tank leak at all.
Water heaters normally have (are required to have, anyway) safety relief valves to prevent an out-of-control heater from turning the water to superheated steam which could be a huge risk. So relief valves are provided – and are not normally “used”, because most water heaters work properly most of the time and consumers just don’t care as long as there is sufficient water at sufficient temperature. But sometimes those valves actually function, and actually do release some built-up pressure, including a steam and/or water release. (Those valves can also be set to operate too conservatively – meaning operating too early, when there’s no need for them to function automatically – and can fail in ways that other valves fail in, too, when they simply leak.)
That valve is more than likely at or near the top of your tank and may be one that you’ve identified as “lever action”. (You may not even have identified it as a valve. Here are some example photos from Google.)
Aside from that, however, it is also possible that your cold-water inlet to the heater may simply be allowing condensation to form on the outside of the inlet pipe, which coincidentally finds a drip path to the floor, settling under the heater. In that case the best thing to do would be to apply some light insulation around the cold-water inlet, which just prevents the warm ambient air from contacting the cold pipe, causing that condensation in the first place.
Otherwise, if the tank did leak and you know it, and it’s now not leaking for mysterious reasons, then @filmfann is probably correct in his analysis, and the tank should be replaced or repaired. (There are repair tapes and sealers that will do the job in a pinch and will last for a long time, too. If cost of the repair is an issue a trip to a hardware store may be quite illuminating.)