There are a lot of techs who are intimidated by this form of assembly, and I am sure some of that is also due to how AG carefully conceals the finite details of the amplification stages throughout. Truthfully I find it easier and more enjoyable working on his work compared to modern components because they have a sensible flow to them where a schematic isn't necessary. Most of the gear I get in for repair (newer components as I am also a warranty tech for a number of brands), do not have schematics or service manuals, and when many new PCBs have multiple layers, trace work can take me hours.
The silicone isn't a pain to work with at all. Once fully set, the silicone is a complete solid and does not become gummy with time. AG did experiment with a couple other mounting adhesives in the past that did not hold up as well, and I imagine is one of the main reasons for using silicone throughout today. It works very well and lasts.
Funny that you mention the hybrid amps, as I have a BC202 here that I hope to finish repair on this week. Over 20 years old, still fully serviceable and upgradable. Silicone that I had to remove I simply cut off, and replaced once I was done in that area. The adhesive around the tube section was some of the adhesive I spoke of that didn't fare as well, this was removed and replaced with silicone as well.