Bingo!!
If ANY part is 'touchy', it is the cryogenics. Early heat seekers would often take off for the SUN!! Military jets using afterburners were easy to shoot down. But modern Fan Jet technology bypasses most air around the nacelle to mix with heat sort of like we do with Stealth.
Cryogenics either use some form of Peltier solid state heat pump, or the older Stirling Engnie in reverse. Either way, they have to be maintained.
Still puts out enough heat to attract a seeker head, even if you're talking about a passenger aircraft. A turbo-fan fighter engine will put out just as much heat as a turbo-jet engine will - especially when you go into augmentor.