Check your household insurance poiicy, you are more than likely covered to have the tank replaced.
In-laws had leak and tank toppled over (somehow) in their case a specialist team had to come to sort it out but was completely covered by their insurance policy (nothing special about their policy), it took weeks to clear the oil.
Hope this helps, IMO it's best to replace the tank (asap), frost etc and then heat in the summer will takes it's toll and then you will have a larger problem like above !