We were in the trailer last weekend when it started pouring rain. Water started dripping into the trailer around both skylights. I went up on the roof after and I can see how the roof sealant is crack...
Definitely remove the old sealant first. I notice that on any tube of Dicor sealant the preparation instructions always say to carefully remove the old sealant. I wish I knew how that was done because that sealant seems to engage in a tug of war with the EPDM membrane anytime I've tried to remove it. :M Good luck.