RV Repair: RV Roof Repair, seam tape, rv roof

Question
Hi Nicholas..
What is the best way to go about repairing the roof seams on my Dad's 89' Southwind 32'. I have tried the sealant but all it does is crack. The local RV Repair shop here said that this stuff is no good and they will remove it and replace it with a new "seam tape". Do you know anything about this or what would you recommend? I know this info is vague.. but I am trying to help my 76 year old father with this problem. Any help at all would be appreciated.
Regards,
Rick

Answer
The most important factor in what to use is what the roof is made of. Also, what does the sealant on the roof now look like(is it metallic, white, stiff and brittle, soft and mushy?) Does it crack across the middle of the seam or chip off from the edges?