Yeah, but there are many good options. Magnetic alignment can keep things from touching most of the time, maintaining very good movement without friction. Graphite is a great lubricant and works even in very cold environments, not to mention it will not be all that cold given the heat passing through the system. Redundancy is also a big part of the design, making failures much less impactful. And using sterling engines for the highest draw part of the lifetime of a probe with peltier style generators there for later would allow a failover to a solid state system at lower efficiency.