Greg,
Do you know how many miles are on the engine since its last overhaul? As you have surmised, the rings on #5 may be somewhat tired, and the rest of the cylinders are slightly low. I recall seeing 130 to 140 psig on good 235s, and I get 230 psig on my 261, with 11:1 compression ratio. However, unless you want to rebuild the engine for other reasons, there is no immediate need for an overhaul.
By the way, was the throttle plate blocked full open when the engine was cranked for the compression test? If the throttle is closed, the manifold pressure will drop and the peak compressed pressure will be low. This will probably have not much effect on the difference between #5 and the rest of the cylinders.
Good the see another St. Louisian active with a stovebolt.
Hoyt
