Compression test each cylinder?

 

That won't help if the leak is into the pushrod chamber. A leak down test would give a more accurate diagnosis, a competent shop should be able to do it for a reasonable price or sell you the tool if that is more practical.

 

If its leaking from the chamber you can normally hear it when you try to start it also. A bit of a puff, or whistle sound as it trys to start. Also look for oil leaks around where the head joins the block. Frankly I have never suspected a head gasket, and found it not blown when I took it apart.

 

If you have a leaking head gasket, one would think the pressure developed while cranking would be lower. Even with a working compression release there should be a pressure differential between cylinders.
Unless the leak is into the crankcase, as some B&S engines regularly display, there likely would be external evidence of leakage, such as black smudges where the partially burned mixture leaves carbon trails, or oil seepage(less likely), or even the tk-tk-tk sound of the combustion gases being forced past the leaking gasket.
If it leaked into the crankcase, oil would likely be forced out to where it would not normally be, such as past the dipstick cap, the dipstick seal at the crankcase level, the rocker arm cover gasket, and also pushed out through the crankcase vent and fed to the engine via the carburetor. Some may foul the air cleaner element depending on where the crankcase vent is connected.
B&S seems to almost have the market cornered on blown head gaskets. They leak into the pushrod chamber and then the crankcase(connected). Apparently the span between head bolts is a bit too long for adequate compression to hold the gasket firmly and prevent distortion and leakage. Other engines... not heard of so much.
tom