Tach cable spewing oil

My tach cable has recently started spewing oil. Presumably the seal is gone. Are these still available anywhere but ebay? Are they model year specific? Does the valve cover have to come off to replace it?

Should come off without removing cover. Remove the retaining screw/bolt and lock-plate, then thread it out.

Awesome. Thanks. Now to sort a few other problems.... like my carbs acting up and it suddenly not charging.

I had the same problem, so while I was looking for and waiting for a new seal kit (zedparts.com based in the UK)
I decide to see if I could at least reduce the amount of oil,
I found an old generator gasket and cut 2 of the projections for the bolts to pass though so that they would fit into the top of the tachometer pinion and sitting on the oil seal,
I place the first in position the second I attached a 6mm S/S washer using an epoxy glue, after placing this in place I refitted the Tachometer cable, as the cable is screwed into position the ferrule on the outer cable compresses the oil seal.
It didn't slow the leak, it actually stopped it, its not the correct way of sorting an oil leak but as 15 minute temp repair it worked for me

Is it coming from cable? Mine did and just fitted a couple of other rings between nut and cable outer. Worked for me

There was so much oil you could not tell where it was coming from, but my solution sorted the problem , I have a seal kit now so when it leaks again I will change them