It's so, so grim 
All of a sudden there is a stench of stale urine from inside the bowl, more from the front (I've had my face closer than I'd have liked - boak). I can't see any damage and it was new in 2008.
I recently swapped bleach for Ecover toilet cleaner. Could it be that not doing the job?
I've currently got the seat off soaking in a bath full of flash but I'm sure it's not the seat.
Any ideas?