A compression leak is definately going to kill low end. The lower RPM range is where the engine needs higher compression to develop any sort of power. There's also a danger of overheating at high RPMs if the head leaks. So, it's a good idea to cure the head leak..
I don't think some kinda gasket maker is the way to do it. It sounds like you still have the gasket and it's not cracked.. if it is damaged, see below about making a new aluminum one.
If the head and cylinder surfaces are flat and if the gasket is intact and if the head bolts are torqued properly, there should be no leak from there...
Find out why (and confirm from where) it's leaking before doing anything else. Put a straight edge across the head surface .. use a torque wrench on the cleaned bolts/nuts/threads and see if everything's snug. About 10 pound feet is average but some mopeds use as little as 5 pound feet, so be very careful. Got an owner's or service manual with torque specifications?
Do a compresssion test. Other possible points of leakage are anything above rings and including the rings.. decompression valve (if there is one), or a cracked head, damaged head surface, loose spark plug .. etc.
I don't know what the Solo uses for a gasket.. it's common to find a thin aluminum head gasket. New ones are easily made from some sheet material of the proper thickness you may find around the shop.. or in a hardware store. Get as close to original gasket thickness as is practical.
Nothing special about the aluminum alloy.. something soft is good. A softer metal conforms well to the minor surface defects of the head and cylinder. Aluminum flashing for gutters and roofs would be OK if thin enough..
Clamp the sheet between two pieces of wood to drill clean holes. Cut the gasket shape with sharp razor blades and scissors or whatever .. Preferably a Dremel Mototool or any little highspeed grinder with cutting wheels. Little grinding wheels to clean everything up..
It's easier if the inside of a gasket is cut out before the outside is trimmed off.. Be accurate about bolt hole placement.
More might be suggested if you provide some details about the head gasket and nearby elements.. overall condition of the engine and the history of that bike..