I am suspecting my gasket is blown cause im losing coolant rapidly and my oil cap has some "mayonnaise".

1. what causes gasket to fail?
2. roughly how much should i expect to pay to get this fixed? (my warrantee covers me for R 3000.00 on gasket only)
3. must i replace waterpump and thermostat?

 

Do not drive it.. The coolant mixing in the oil will kill the bearings if it hasn't already. I'm not sure what the cost will be, you'll have to get an estimate first. It's not going to be cheap though knowing how most shops charge these days. Go ahead and replace the waterpump and thermostat if you have it done. It's an extra $60-70 but since the timing belt and such will have to come off to remove the head, you might as well change them out while you're in there. I recommend replacing the waterpump and thermostat whenever you do a timing belt change regardless.