Just a few weeks ago I repaired the floor on my older Willy-1:
Mine was leaking at the perimeter of the inflated portion of the floor...also some longitudinal cracks running across from being rolled. inflate the floor and rub soapy water on it to find even the smallest leaks.
I contacted Maravia and explained the problem. Their customer service was great (I bought a used boat that had run commercially and they still took the time to walk-me through the repair).
I ended up with bias tape straight from Maravia (Cascade, their retail arm) and Clifton's glue... some of the tape was cut to 1 1/2" and some was 3" wide.
Lots of MEK (nasty shit) to prime and clean, then a couple passes of glue. a heat gun is great.
now, the floor is holding air for about 24 hours before it needs to be topped off.
also...if you ever want to trade your willi 1.5 for the (14') willi-1 let me know!