I think he said "forced landing due to loss of GPS". Sounds like control of the drone was an issue. Someone just posted a pic of the Karma taking off the top of their finger in another thread. Not sure saving the drone is worth the risk.
"Arms" for the Karma are about $50 on Amazon or you can purchase them directly from Gopro. They are easily replaced and Gopro publishes DIY videos on Youtube that show you how.
Hopefully, you can figure out how to clean the motors without buying new ones, but I thought I would mention this as an option.