On the Shoe-Goo/Sugru issue: Both are good options, in my experience. Shoe-Goo in black is not easily available in Canada--seems we have only the "clear" (actually translucent, foggy) colour, so I had to buy some of the black stuff from the U.S. via eBay.
That has other uses for a cyclist, so it's worth the expense. Make sure you seal the tube & cap well after use.
Silicone-based sealants--e.g. sealants for exterior household applications--could work for things such as twist-grips, but you would need a sealant that dries to a firm (but not rigid or hard) consistency. Otherwise, you could find it so sticky that it's hard to get your gloves cleanly off the grip.
(Householders in Eastern Ontario spend a lot of time fussing with sealants, to keep water/snow/cold winds/etc at bay, so we have a range of options at most hardware stores. A look at the Permatex website should yield some ideas, although maybe not every product there would be available in the UK or Europe.)
