Having worked two certifications for cold qualification, I have seen that these are the places that get the most attention:
1) Servo seals - which shrink horribly when cold soaked to about -32 degrees C, and make the hydraulic system leak like a stuck pig. Especially servos around the shaft seals. When warmed back up, no problem, they seal right back up. The newer seal materials work down to about -42 degrees C, if your aircraft is fitted with them. The RFM limits are the key, of course.
2) Elastomerics, especially in the rotor head. They do not like to be stretched too far when cold soaked, but they warm up very quickly, which is the reason for warm-up times without moving the sticks on some helos.
3) Cockpit displays, especially the new liquid crystal, which stay blace until they warm up. For super cold operations, there are sometimes heaters installed to get them up to temp so you can see the gages to start.
In general, there problems are in cold soak, and are not problems when you fly a warmed up helo into temps that cold (like that silly movie 'The Day After")