Mine's the same, can't see a bloody thing whatsoever anymore.
So i played about with an empty sump, gradually pouring over 3 litres in whilst watching the glass and there was no change at all. Now i just put in a bit more when new and ignore it 'til next time. Fortunately it doesn't leak and i have never needed to top up between 4000 mile changes, so i'll just let it be. Looks more trouble than it's worth to change.