heat is not what is killing the crank. It is either lack of oil or lack of proper storage. Now that these are older sleds, the lack of proper storage is adding up. People do not block off the outlet of the exhaust when storing. This leaves one cylinder open to atmosphere.
Heat on the problem bearings is a non issue. Think of what is right in front of those two cylinders on the case. The water pump housing. All that cold water is flowing over the front of the case. On vipers and srx sleds this water is somewhat a constant temperature as unlike a car, these sled us a mixing housing for thermostat. There is always water flowing around even when the stat is closed, when open, now you have hot water and new cold water mixing coming in, the more the stat opens, the more it closes off the hot water mixing port and goes to cold only water. Great system, quick warmup and no sudden influx of cold water to stress the motor.
The other part of the hot crank that doesn't add up is this. The motor is nothing more than a combination air pump and compressor. the compressor is on the top side and is where almost all of the heat is generated. the lower section (because this is a 2 stroke) is the pump part. All of the air, Cold, comes rushing into the engine with every rev. The first thing it hits is the top of the case, the crank and the rod. This is what keeps the crank and cases cooled the most and is why you don't see manufacturers wrapping a coolant port around the crank case. It is just not a big heat issue to start with. crank cases of 2 strokes are air cooled by their own cycles.