On our H54#50 we removed the galley roof panels to get to the back of the engine panel. The bulbs just pull out of friction holders. Takes a minute to replace them, an hour to reassemble the galley ceiling!
Not sure about the gauge cleaning. They may be sealed units and you might have to replace. See the Engine parts catalogue for all this stuff so you can order the right parts.
FYI the parts catalogue is very useful not only for getting parts, but also just to show how things fit together in the exploded diagrams. Way more useful than the users manual!