I made a hole in the crankcase at the last replacement of rubber barrels (October 2015) to provide a ventilation of the crankcase in hot weather, it will perhaps improve the problem of lifetime of rubber, it may extend the duration of life of the rubber, no temperature measurements before and after the assembly of the fan except
put your hand on the centa casing which seems to me less warm by putting your hand on the casing after one hour of traffic in slow motion.