I could be wrong but it sounds like he may have some "boar glue" stuck on him (semen). It could either be from him or, if he's been kept with other boars, quite possibly from another pig, which can sometimes happen. Boar glue usually sets very hard, so if the sticky stuff you've seen is starting to set then I'd try to remove it asap, if not already. It's perfectly normal for boars to occasionally get this 'glue' stuck on them (some more than others though) and nothing to worry about - just carefully snip it out with scissors if it's set hard.
Otherwise it may be a bit of excess grooming fluid perhaps, although I'm not sure if this is sticky stuff as it usually gets wiped away very quickly. Guinea pigs naturally excrete a milky white liquid from their eyes (looks very odd when you first see it but it's completely normal!) which they use to groom themselves. They wipe it around their hair with their front paws so that may be what you've seen.
Obviously it could be something completely different though, so keep a very close eye on him. Discharge from the nose is not normal and eyes should also be clear, so any other discharge from the eyes (apart from the milky grooming fluid) needs looking into. Also check his skin as thoroughly as you can, in case he has an infected wound.
Obviously it goes without saying that if you're very worried you should always see a Vet for peace of mind. It's not a bad idea to get new pigs a check-up anyway, just to give them the all clear.
Good luck x
