mineral oil on thermocycler block

[Marcelo Carnier Dornelas]

Hi netters

        I've seen people using mineral oil on thermocycler block to 
increase heat transfer to the tubes. Is this necessary? Doesn't it 
reduces the lifetime of the thermocycler's block?
        Thanks for any comments
        
                        Marcelo Carnier Dornelas
                        Genetics Department
                        University of Sao Paulo
                        "Luiz de Queiroz" School of Agronomy