I wondered that myself a while ago. I read that he became a recluse and is now in a retired actors home. It's a shame. I got this info here http://www.imdb.com/name/nm0642801/
There are some posts on what he's up to now on the message board.
Richard O Sullivan is currently living in Brinsworth House in Twickenham Middlesex where Alan Freeman lived until last week. This is the home for retired performers and is partially funded by The Royal Variety Performance. Charlie Drake also lives there as did Thora Hird for part of her life.
Anyone remember his stint in the ITV 'Doctor' series? He played nerdy Dr. Bingham and was very funny. I never really liked him in Robin's Nest though, thought it was a bit lame. Despite that, sorry to hear he's that unwell.
he had a bit of a drink problem as well at the end of 80's apparently - I used to work in Richmond with girl who knew him its a shame- how old would he be now?