This question concerns a 1999 UK Ford Focus 1.8 Petrol model (ZETEC E)

I know from various sources how bad it is to get engine oil etc onto the timing belt and tensioner etc, e.g. from the Hayne's manual and various internet articles.

On the one hand the thought is that there could be oil on my timing belt from a rocker cover gasket oil leak and so this could reduce the life of the belt or if it slipped on the idler pulley could cause great engine damage. On the other hand I think about all the car/vehicles on the road today that have timing belts and especially the older ones which are probably contaminated with oil etc from leaks of one kind or another but they don't seem to worry about the financial consequences of a belt failure.

What are your opinions on this situation ?

I have to say that i do share your concerns. Oil on the belt will surely perish the belt at an alarming rate. As a general rule of thumb, if i discover any signs of oil or fuel for that matter, on the belt i tend to get it changed as the cost of this is a small price to pay as an initial outlay which could lead to a very substantial sum to fork out at a later date.