What results would I get if, once fully charged, I trickle charged the SLA battery with a constant current of 5ma?

 

Sla batteries should be charged with a constant voltage.

 

They don't do constant current. Charge at about 13.75V and they'll pull the necessary current to maintain their charge.

 

The self discharge rate of an SLA is 1% per day. That's 0.54 ma x 24 hours.
Pour 5 ma into it, 24 hours per day, and you will just lose the water in the battery.
Battery university shows 13.5 as the "right" float voltage.
http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

 

Back in ancient history, when I worked on the development of large Calcium place lead acid batteries (2 volt 1680 A-hr cells, generally for telecom use) we used a float voltage of 2.17 volts per cell. Supposedly, this would keep the cell fully charged with minimal loss of water. 2.17 v/cell * 6 cells = 13.02 volts float.