This same exact thing happed to me while I was troubleshooting a school which had lights that were blinking. The bottom of the Current Transformer (CT) cabinet was completely rusted out. The CT's were barely hanging on to their supports. I quickly had to throw some wood in the bottom of the CT cabinet to support everything, get the POCO lined up and other EC's to help change out the service. The cause of this was the POCO never sealed the end of the service pipe. The ran underground for about 60' then turned and ran straight up the Telco Pole. There never was a service head or even duct seal applied to the end of the conduit. The rain water would run down the pipe and exit into the basement of the school for many years until the bottom of the enclosure fell out.
I find this all the time on resi jobs. The bottom of the loadcenters get all rusted out. Many times the CB are also corroded, some are stuck in the on postion. Service cable gets a little hole in it and lets the rain in, cable assembly acts like a hose, drips down into load center, sometimes days after the rain. The other one I see alot is dried duct seal, water drips over the lugs in the meter down into the lower cable into the load center. Weep hole will not prevent this. It will make it more noticable, when water drips on the floor.
It has been a long time since I saw an SE job but they were popular in Md. I remember they always had a drip loop in the SE between the meter can and the penetration into the house. I may still have some pictures of my service up there somewhere.
Around here it is virtually always a straight back to back with a short nipple between the load center and the meter can.
You would need an inch or two of water in the meter can to get to the nipple even in the lower KO. FPL gives us aluminum meter cans and the way the cover goes on, water will run out the bottom.
There was a job here in NJ where the HO had a new service installed. Later that year later he had the house sided with new siding. The siding installers just yanked the meter pan off of the house and left it hanging. They never attached it back to the house. A year later I came by and found that there was water coming into the service panel and ruined the whole panel board, main bus, and CB's inside of it. He had to get a whole new service again, I couldn't save anything from the original service.