Farkas won't offer me the option to do a mission for the companions, despite the target mark pointing me to him. I have finished the main quest-line for the Companions and can still get jobs from Aela, Vilkas (and the resurrected Skjor)... but Farkas will NOT offer one.

Anyone else have this problem?

I had the same problem but with vilkas instead. Sadly i just gave up and used the console command to cure me of the illness.

What I wouldn't give to have the console in these times of need !

Yeah I have this problem with Vilkas. Nothing to do but ignore it for us console players.

I had this problem but eventually he started offering quests again.

I will keep at it.

Currently trying to get Aela to offer me the Totems quest (stayed a Lycan for it specifically) and she keeps giving me Animal Extermination... and I didn't even marry her [even though she is marriage material, yub yub] !

I had an issue with Farkas wherein everytime I entered Jorrvaskr he would immediately draw his sword and open the dialogue box as if I had tried to speak to him (he wasn't hostile, but he drew his sword). I just loaded an earlier save, did a few other quests and it cleared itself.