"Is the normal operating reliability reduced by the 30 minute run dry regulation? For instance does the 30 min run dry requirement result in more fancy materials and are those materials just as reliable as those used in a similar gearbox without a 30 minute run dry capability?"
Droopystop,
There are two different issues you may be confusing- reliability and fault tolerance. Reliability is the statistical failure rate of a particular component or system. Fault tolerance is the ability of a system or subsystem to tolerate faults/failures and maintain function.
To answer your question, achieving a 30 minute loss-of-lube capability in an MRGB usually involves (among other things) adding redundant components/systems. All other things being equal, adding more components to a system will naturally decrease the overall system statistical reliability rate. However, at the same time, adding that redundant hardware may also increase the system's level of fault tolerance.
The biggest problem with loss-of-lube in an MRGB is overheating of the highly loaded gear teeth and bearings. Impinging lube oil flow is how these parts are normally cooled, since they have very limited conductive heat paths to structure. If there is no cooling oil flow, the gear teeth and bearings will build up heat. Standard gear (9310 steel) and bearing materials (E52100) are capable of operating at temperatures around 350degF max before their heat treatment begins to be affected (de-tempering), weakening their structure and eventually causing failure. There are high temp gear (X-53) and bearing (M50NiL) steels, and these can operate up to temperatures of about 600degF. But these materials are currently somewhat more costly than standard materials.
Taking into consideration only the material itself (and not heat treatment, processing, manufacturing precision, etc.) with regards to reliability effects, there should not be a big difference between standard and high temp alloys. Reliability factors of gear and bearing steels is based mostly on their metallurgical cleanliness quality (low presence of inclusions), and double vacuum melt quality is always used regardless of the alloy.
Hope that answers your question.
riff_raff