I cracked my 2015 Jekyll purchased from Pauls (its documented in the Pauls Cycles PAS thread).
Cannondale Europe wanted the full bike for inspection but I argued that I was transferring the parts onto another frame as I had a road trip booked & paid for. A few pics of the complete bike and they were then happy to receive just the frame.
Warranty return took 3 or 4 weeks and I received a 2016 frame back. If you do send just the frame make sure everything is removed – i left the rear caliper adapter on the cracked frame and it wasn’t returned – i had to chase it up.
Otherwise no complaints, good comms with Pauls.