I have an old farmhouse with a mansard style roof with steep main roof areas and a fairly flat area at the top.  I guess this is a victorian architectural design.  The roof has four inside and eight outside corners.  The roof was totally redone 20 years ago and  “w”  type metal flashing was used in the four valleys.  These were never a problem.  Recently the roof was done again.  The old shingles were removed.  I didn’t watch the roofers constantly so I can’t describe all of their tecniques perfectly.  They reused the metal valleys with my permission.  They assured me that they were in good shape and they would paint them to help keep them from deteriorating.  I don’t know if they removed them and used underlayment under them or if they kept them in place and roofed over them.  At least one of them leaked right from the start.  It is facing the North East and our prevailing wind is from the South West so much of the rain is blown to that valley.  I put a lot of roof patch on the valley to stop the leaking but now would like to fix the valley so it will not leak and remove the patching material because of the negative esthetics.  I had little choice in the matter since we were in a very rainy period and the leakage was causing dammage in the house.  I would also check the other three valleys to ensure they will not leak.  I believe they have but only slightly.  The question is: What would the best method be to repair the valleys, keep them from leaking and restore proper esthetics to the house.  I would be happy to discuss why the roofer wasn’t made to return and fix the problem areas but that is quite a long story.  I didn’t think I could put that information here because I would want to put in the names of the contractor and sub contractor and that probably wouldn’t be acceptable.  Please give me some advice about how to proceed with proper repairs.