sanded wings
Couldn't agree more with point k.
Highly polished wings through a rain-shower leaves a highly-polished wing covered with drops and you instantly lose half your glide performance -as well as 5kts of minimum thermalling speed. It's like having three flattened bugs per square inch.
Smoothly roughened plus dried detergent is the only answer.
Once went cloud flying with a turn and slip that'd had the pos/neg power hookup reversed. That sure smartened up my learning curve. Went out and bought an ex-Lightning Ferranti Mk 6 AH after that (and I've still got it - going cheap if anybody wants one). Wifey made me sell my super sailplane to buy her a new car.