I have got a Snes which is in pretty good shape. My problem is that the RF jack is very dirty and corroted. I haven't tried cleaning it because I think I could accidentally break it. (The jack is working perfectly)
You need a contact cleaner. Wikipedia does mention isopropyl alcohol as being one, but I've found that the industrial products designed specifically for contact cleaning do a much better job.
I currently use Kure Contact Spray; a quick spraw of it causes oxidation to visibly vanish. This exact product doesn't appear to be available outside Japan, but the label has the trademarked "CRC" logo on it, so it's probably the same as or similar to CRC QD Electronic Cleaner or another CRC product. There are many products designed for cleaning electronic and electrical contacts; just search for "contact cleaner" on your favourite shopping site.
Note that some vendors offer different products for removing corrosion and protecting against corrosion. Back in the 80s I used Cramolin Red to clean contacts on audio equipment; there was also a Cramolin Blue for protecting contacts once they were clean. These are no longer manufactured, but Caig, which I believe was their manufacturer, suggests that DeoxIT D100L and PreservIT P100L are their replacements. There's also a discussion from a user on the history of these and which product should be used for what.
Well, I tried the methods recommended. I cleaned it with some Isopropanol. The corrosion isn't gone but I guess it's better.
Perhaps a scratch pen ?
I've successfully used one of these for cleaning contacts inside a camera, where the corrosion has been due to leaving alkaline batteries in until they leak.