Yep, had that same oil leak problem in my spark plug recesses. Wiping out the two or three affected recesses and cleaning up oil contaminated plugs and boots became a routine chore. Mine did turn out to be the valve cover gasket. There's really no other way (such as cam leaks) that oil can get into those plug recesses. As Bill mentions, keeping the PCV flame trap clean can help, especially if it's the old coil style. The plug boots can be a bit of a bear to get out -you certainly don't want to pull on the wires and grabbing the top with pliers can split them. I never did find plug forceps that could get in there deep enough to grap the end of the boot. Again as Bill mentions, lubricating inside the boot and around the plug ceramic can help. The proper stuff for the job is dielectric grease. Use it on your distributor boots as well (keeps out moisture as well as making them easier to remove).

A new OEM valve cover gasket with proper torquing may be all that's needed. When new, lightly torque the valve cover nuts to the spec'd 11-12 ft.lbs. in a cross pattern starting from the middle out (as you would for a head gasket). Re-torque at the next oil change. If replacing the valve cover using on old gasket, I used to increase the torque to 12-13 ft.lbs. (still a fairly light torque). Naturally make sure the cover-to-head mating surfaces are clean. Although it's a cast rather than stamped cover, if the valve cover has become the slightest bit warped (possibly due to improper torquing), you may need to apply a little blue RTV to the valve cover gasket around the spark plug recesses.

While on the B234F head oil leak topic:

The back edge of the valve cover around the cam journals seems to be another area prone to weaping oil, but you often won't see it unless you're working behind the block or chasing the post-nasal drip of oil on the bell housing. To help eliminate that you can apply a little RTV along the back edge of the gasket over the camshaft carrier caps, especially in the corner areas. Also do the front edge if needed.

If the distributor shaft seal gets worn it can become a source of oil leaking down the rear of the block. This is a wear item and occasionally needs replacing. If you keep your engine clean and occasionally blot a paper towel along the unseen areas around the head it's easier to find oil leaks, as is a well lit inspection from underneath.

Any oil weeping out around the camshaft carriers will be at the front and rear of the block. This shouldn't be common if the camshaft was installed correctly. For the front and rear camshaft bearings only, the mating surface between the camshaft caps is supposed to be coated with a thin film of RTV or high temp silicone sealent before the cap is installed.

My B234F also developed a minor oil leak at the head gasket and apparently this is not uncommon as the gasket surface around the oil passages is not overly wide in some areas, especially on the exhaust manifold side.
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Dave -own 940's, prev 740/240/140/120's & quasi-expert only on a good day