Well, you can add me to the cracked RH4 group. I just checked the head on the MK3 that I'm rebuilding, and discovered the dreaded crack at one of the intake guides. Its visible without the need for dye penetrant checking. It looks about 3/8" long, but might be longer if checked properly. Supposedly, the bike had around 20,000 miles when it was torn down and put in boxes, which is how I got it. The other port doesn't show any cracks to the naked eye, and it didn't seem worth it to do the dye penetrant check. Fortunately I have an RH10 head off a race bike that looks pretty good, other than needing exhaust thread repair and stud inserts. More work for comnoz. I have another MK3 that I'm about to tear apart, hoping that the head is ok. Sure would be nice to find a method to repair these heads. Must be a lot of them out there by now. I would consider trying to weld it, but I haven't had really good luck trying to weld on Commando heads, other than for fin repairs. The castings tend to be really porous, and you can never seem to get all the oil out. Those Fullauto heads are looking better and better to me.
Ken