There are several things that are going on with Buddy. First of all, the feces problem is called anal impaction. Many males who are not neutered get that when they are older as the muscles of the anus weaken and stretch. You are treating it exactly the way you should by removing the ball of feces. Having gone through this with one of my own guinea pigs, I agree about the odor. My way of dealing with it was to get one of those swimmer's nose plugs to wear while doing this.
The head tildt and coordination problem sound like an ear infection, although I'm not sure what the jumpy eye is from.
You definitely need to take Buddy to see a vet, preferably an exotic vet who is used to seeing guinea pigs.
For more information about Anal Impaction see:
http://guinealynx.info/impaction.html
For more information about Ear Infections see:
http://guinealynx.info/emergency.html#ear