Bailey,
I maintain a total of 8ea 100AH Sealed Lead-Acid batteries, four in an industrial scissors lift, and four to run my ham station on.
The correct float voltage (printed right on the battery) is 13.6 to 13.8V, about 700mV higher than for a flooded-cell lead-acid battery. You are right, the self-discharge rate of a SLA is about 1/3 to 1/2 of what it would be for a comparable size flooded-cell. On float, after they are fully-charged, I see a long-term leakage current of 35-85mA on the 100Ah SLAs at room temperature. As they age, this current keeps increasing. By the time the leakage current is over 120mA, the battery is ready to be replaced.
SLAs are even more prone to damage due to chronic overcharging than flooded-cell batteries. You cannot replace the electrolyte, and their grids are also subject to corrosion.
Read the warnings about overcharging on the SLA maker's spec sheet. They are very emphatic about it, and they will not honor their warrantee if they inspect a battery, find the plates corroded due to overcharging. (Ask me how I know)
An unregulated 0.4A(ave) constant-current solar panel will overcharge even a large SLA if you are relying on the self-leakage of the battery to consume the available current, precisely because the leakage current is so low to begin with.
Get some of
these: