 In such instances, engine oil will readily react with the sulfur in rubber components, hence quickly degrading coolant pipes and hoses to the point of failure.During the porous head debacle, GM faced bankruptcy – therefore dealers failed to recall affected models.Due in part, to the engine's immense prominence and demand, many businesses now specialize in the repair of porous GM "C20XE/LET" heads – by either sleeving the affected gallery or by injecting a polymer based substance into the porous region.