how do I strip off old hardened teak oil residue?

It may have been a type of teak oil called Danish Oil which does tend to leave a residue.

I would use meths/white spirit to loosen the oil and wire wool to scrub it off - coarse wire wool to begin with and perhaps 0000 grade to finish - then maybe 400 grade sandpaper (only because I have some of this grade) wipe up with white spirit and when dry brush down and vacuum clean at the same time - then proper Teak Oil. I have never been able to overdo Teak Oils application - it always soaks into the wood and never leaves a film and I'm very liberal with it because I got 10 Litres free - shop around for your Teak Oil and buy in bulk - small quantities are sold for silly money.

http://www.decoratingdirect.co.uk/viewprod/b/BIRTO/

Good luck...

Peccavi
December 2009