Thanks, that sounds reasonable. One thing though, the previous owner said he did oil the fretboard last month so I don't want to overdo it. It should be fine though you think?I dare say a toothbrush, and some isopropyl alcohol should serve you well. Then polish the frets with your choice of materials and technique, and then condition the fretboard with your choice of fretboard conditioner.
Not sure if that's it but I've seen green gunk on fretboards a few times and always it was because someone used food grade oil. The moisture from sweat will turn oil like sunflower, olive, etc. green. The last time it had a very noticeable smell from going rancid too.