Is it safe to assume that when Bentleys says "single-carb" they are referring to the Type 1 engine? And "dual carb" means Type 4? Or is it more subtle than that?
If I have the Type 1 engine, which I guess is what Bentley's calls the "single carb" engine, what you say about replacing the covers matches up with what Bentleys says: no can do with the fixed-length types w/o pulling the engine and head.
But can do with telescoping covers and by removing that mysterious and wondrous assembly called the rocker arm and setting it aside. Probably on the lawn here. Then the pushrods can be slipped out, cleaned and used by the kids for lawn darts while we somehow pry the leaky pushrod cover loose (pound on it with a hammer and bend it, pinch it with vice grips and pull it out?. The we smoosh in a new telescoping one. Next, find the kids and have them bring back any missing pushrods, and install new silicone rubber seals (per Bentley, "single carb" engine, therefore Type
1) and slide the pushrod(s) back in place. Installation of the rocker arm assembly is, as they say, the reverse of the removal procedure with the exception of making sure that all the grass clipping have been wiped off it.All of this is purely academic because I don't yet know if my leak is a leaky pushrod cover. I just got hung up on the Type 1/Type 4 vs. Bentley's "single carb"/"dual carb" nomenclature.