| if I was you - and as you say its been recently greased - I would CAREFULLY use a samll drill bit - drill a tiny hole in whats left of the bolt - get a tap slightly bigger than the hole you have just drilled - and start tapping into the hole - then try and reverse out the bolt by unsrewing the tap.
this sounds crazy - but its worked for me several times - the last time being a siezed and shagged Ti bolt in a rearset - a tap usually snags nicely on a new thread it has just cut.
Khushy | 
Threaded Mode