Pete, for what it's worth an evolution of design and cost cutting. A7 Longstroke and the early Plunger cases share the same breather external pipe, depositing oil mist onto the chain (via a small bleed hole) and onto the road and garage floor as the pipe was originally secured to an engine through stud behind the sump plate. Late Plunger engines have a small pipe directing breather mist to the gearbox sprocket, anchored beneath the flat alloy extension/chainguard front mount.
With the advent of the S/A engine, some retain the same type of early pipe, exiting down by the sump plate, later ones just have a hole, presumably as the engines could be fitted in frames with a fully enclosed chaincase and the pipe would be in the way. The oil mist lubricates the fixed front chainguard section, which is why many survive.....or because lots were removed.
Your option is to enjoy the oil and muck of yesteryear or counterbore the hole for a spigot and add a flexible pipe to allow oil mist to lubricate the chain or just drip.
Swarfy.