Generally, when choosing a material like this, these are the factors we're interested in:
- Neutral-cure silicone. A lot of hardware-store 1-pack silicones are acetoxysilane based which will release acetic acid in the curing reaction, which will corrode nearby things - you don't want this, you really want a neutral-cure silicone. This is probably the most important thing, and if you can buy a neutral-cure Home Depot silicone for a couple of bucks it's probably fine.
- One-pack, because it's more convenient than mixing a binary system.
- RTV (room-temperature vulcanising), i.e. it chemically sets and crosslinks by itself at room temperature, going hard with the desired shore and mechanical properties.
- Has some "bounce", which is the main motivation for choosing a silicone over a polyurethane.
- Cheap and locally available for you in a non-bulk pack.
- High dielectric strength, although if you're not using it for HV applications anything is probably fine.
Personally, I like Dow Corning 738, which is available in a small tube.
It's actually documented as an engineering material - it has a datasheet, and if we want to know, say, the dielectric strength, it's documented.
https://www.ellsworth.com/products/by-manufacturer/dow/sealants/silicone/dow-738-electrical-sealant-silicone-white-90-ml-tube/