My 2 cents: like MCRider, I saw head leaks on the K0 and early K1, which were usually "fixed" by either retorquing the head or installing a new head gasket. One of the prime suspects was under sized O-rings at the 2 up-going oil passages to the head, which would leak with thin oils and wash away the sealant on the rest of the head gasket, then it would dribble forward and show up at the pipe side. Honda's head gaskets were coated with something like rubber cement, but it was oil-soluble.
Today, I more often find the pre-K3 head (and cylinders) need to be flat-ground, which I do during rebuilds. It adds a little cost, but worth it, IMO. Many have warped, probably just from age and metal curing: a flat-grind will restore them for many years. I have the shop mill about 0.005" from the cylinder deck, about twice that from most heads.
This flat-grind solves accidentally another problem that has appeared in many gasket kits (including Vesrah) in the last 5 years or so: undersized O-rings. They are coming with too-thin O-rings for the oil passages. Originally, the ones in the head-deck interface and the case-cylinder interface were 2.0 to 2.1mm thick: today's Honda fiche list them at 1.9mm thick. This is some sort of engineering mis-interpretation, IMO, because the 1.9 is the MINIMUM THICKNESS that is allowed in these spots. The same is happening in other sections of the engine (and other bikes), complicating the problem. Anymore, I end up going to a seal store, buying 2mm thick versions for these rebuilds. They never leak, then, because I have typically squished them almost 0.4mm more from the flat-grind, and added 0.1m more thickness. In the last 2 Vesrah kits I just opened, one of these O-rings is 1.9mm thick (and pink), while the other is 1.6mm thick (too thin, period!).
The same situation is happening with the O-rings being supplied for the oil jets, at least in the last 2 gasket kits I just opened. They are being sent out with 1.6mm thick O-rings instead of 1.9 (this is a 4.0x1.9 on the outside of K0-1 cam bearings, or 6.0x1.9 on the inners, and 6.0x1.9 for both on the later engines). I have switched to my trusty bottle-full of 6x2 and 4x2 O-rings for these, as outlined in the book.
It is also happening on the O-ring for the countershaft bearing oil passage: use a 2mm thick one there for longer-lasting smooth tranny shifts.
The main oil journal in the (split) cases is the 18x3 size, and the last red-colored gasket kit I saw ("Made in Japan") came with this one at 18x1.6mm. This will cause oil leakage from the main oil journal, which lowers the pressure all through the engine and can make it weep right in the center of the cases, at the front. I suspect this "change" was applied because this same O-ring fits the Neutral Switch, but in 18x3 it is difficult to install: however, not using the 18x3 here will make it leak almost from day One. Makes it worth the effort to install the right one!
I don't now if this is Vesrah's (or the other gasket vendors') "fault", as the little O-ring seal packets in these kits are the same ones, regardless of the gasket vendor. They appear to be packaged by someone else, which is likely where the problem originates for all the vendors. I do know the Athena kits have such bad mismatches that I can't make a leak-free engine from them unless I sub all the O-rings, the valve guide seals, and install gasket goo on every gasket. I don't use Athena, since about 2003.
A side note: I have discovered that the 836cc (65mm bore) head gaskets from the eBay vendors' kits (or individual gaskets, which I have also bought) are THICKER than the Honda head gaskets. In contrast, the Wiseco (Cometic) head gaskets are THINNER than Honda's. So, when installing the Wiseco, no changes to O-rings need be done (but you must cut a 5/8" - 14mm hole for each head seal on the later engines, thru those Cometic gaskets), but when installing the other gaskets, you must use at least a 2mm thick O-ring at the oil feed passages to avoid leaks.
BTW: the Cometic head gaskets crush about 0.5mm to a final 1.0mm thickness at 20 ft-lbs on HD studs, while the eBay 65mm head gaskets crush to 1.10mm thick under the same conditions, quite reliably. Honda's head gasket also crushes to 1.0 to 1.05mm on standard-bore engines with the stock studs and 17.5 ft-lbs torque. It is these tiny difference that make a dry (or not) engine at these O-rings, so think them thru when doing your reassembly!
