My '08 34FK leaked from new. Previous owner put Eternabond over suspected areas, totally ineffective. My repair guy had me remove all of the factory applied sealer. Some of it came off real easy, corresponding with the leak damaged areas. It appears that the surface of the two aluminum pieces that come together had not been prepared properly. My guess is that manufacturing residue (oils) had not been wiped of well enough and the sealer simply did not stick there.
He applied a roof sealer specifically designed for aluminum roofs, in tractor trailers, rail cars and the like.
PM me for the specific product, hard for me to post a link on my tablet.
Problem solved. Leakage around all the fasteners at top of the wall are another issue.