Yup..your correct. Found this copy of a service bulletin for oil leaking past the skulls on the Honda.
Here is the info:
SL #65 6/1/66 HONDA MOTORCYCLE SERVICE BULLETINS
OIL SEEPAGE NEAR SPARK PLUGS IN ENGINES WITH ALUMINUM CYLINDER HEADS
American Honda receives occasional complaints of the tendency for certain models with
aluminum cylinder heads to seep a small quantity of oil near the spark plugs. In some cases,
dealers have replaced cylinder heads in an effort to eliminate this seepage. This bulletin is
intended to clarify our policy in relation to this problem, and to suggest some countermeasures
that we have found to be effective. In cases where it can be confirmed that the spark plug sealing
washers are not leaking, accumulation of a stain, or oil residue, near the spark plugs can be traced
to oil seepage from the joint between the combustion chamber "skull" and the aluminum cylinder
head casting. Since the spark plugs are threaded into the iron skull, rather than into the soft
aluminum casting, this joint must "come to the surface" near the spark plugs. Although it is no
mystery how oil reaches the outside of the engine, it is difficult to determine the source of the oil.
Apparently, oil reaches the joint from the oil-bearing chambers through internal porosity in the
aluminum casting; such porosity is extremely difficult to avoid. Once oil enters the joint, it has an
almost unimpeded leak path to the outside because the skull is not bonded to the head casting.
Our studies have shown that machines experiencing this problem can be graded into three broad
categories, based on the severity; each category should be dealt with in a different manner:
1. A stain or oily residue collects near the spark plugs over a period of several days or weeks.
Seepage of this magnitude should be considered a normal, inescapable consequence of the
cylinder head design, and no repair should be attempted. Customers complaining of such seepage
should be assured that no defect exists; suggest more frequent cleaning of the engine.
2. More severe seepage causes definite accumulation of liquid near the plugs; following a hard
run, oil droplets or streaks can be found on the air cleaner covers, etc. Although a "defect" is not
necessarily indicated by this seepage, countermeasures are often necessary to satisfy customers.
We have found that seepage can be slowed or stopped in the following manner: a) Remove spark
plugs and completely clean the region around the plug holes so that the joint between the skull
and the casting can be seen. b) Using a dull punch, punch a ring of depressions, tangent to each
other, in the aluminum immediately outside of the joint.
3. Liquid oil "bubbles" from the skull/head casting joint, puffs of vapor can be seen when the
engine is suddenly accelerated. In these cases, a definite defect is indicated, i.e., actual
separation of the skull and head casting. In most cases, however, the cylinder, rather than the
cylinder head , is the faulty part. We have found this problem to be most commonly related to
"sinkage" of the cylinder sleeve in the cylinder casting, such that the upper surface of the cylinder
sleeve is below the upper surface of the cylinder casting. When this "sinkage" occurs, the
Honda 250-305 Super Hawk Restoration & Maintenance Guide
combustion chamber skull is not forced into intimate contact with the cylinder head casting and
severe oil or vapor leakage, near the sparkplugs can occur. The recommended repair is, of
course, to locate and replace the faulty part.
Source: SL #68 4/29/66 HONDA MOTORCYCLE SERVICE BULLETINS
I don't think Laverda had the same issues.
my main hobby is making things go fast, and my side hobby is boring and stroking things! (or de-stroking on occasion) I love to get power without going the standard route! 
It's just that the twins are a little bit sturdier, but not better.
