Recently, all three of my Silva compasses have developed small air bubbles, effectively simultaneously. They range in age from about 10 years to a couple of years old. They've been kept in rucksacks and bumbags hanging in my garage, which doesn't get particularly cold or hot, so I'm a bit flummoxed (and peed off) as to why this has happened. They're still usable for now, but if the bubbles get worse (and I've no idea what caused the air to enter the needle housing) there's the expense of replacement. We'll see.
Does anyone else have experience of this? Quick internet search doesn't suggest any real remedies either.