BMW are guilty of the crime of massively under-specifying fork fluid. Aeroshell is simply wrong, and I say this after once biting the bullet and buying a drum of the blasted stuff. You may as well use Dexron III which is way, way cheaper and has about the same viscosity.
At the risk of re-starting an old debate, fluid WEIGHT has bugger-all to do with fluid VISCOSITY which is what actually does the damping.
I recommend Castrol Fork Fluid 10, but if you are lightweight then a 50~50 mix of Castrol 5 and Castrol 10 seems to be good (wife uses this, I use straight 10 and heavy duty R80ST springs as well).
Shocks, as someone else said there are lots and lots out there. If I could afford them I would try Wilbers. If I could find a set in useable or rebuildable condition I'd like to try Fournales. But I have found over a period of 37 years that KONI/IKON provide the best "bang for buck" performance/price wise.
Mind you, it does help that IKON is now an Australian manufacturer and therefore as local to me as it gets. What is important is that whatever shock you buy has the correct spring - if a salesman tries to hand you a box of shocks without first asking you what the normal load of the bike is - walk away, they do not know what they are talking about.
A good seller will enquire as to your weight, the weight of any frequent pillion and how much gear you tend to carry on the bike. They will then generate options for you and you decide which end of the scale you want to compromise. Once you have the spring rate more or less right the next step is to adjust the damping rates - if the shock that is being attempted to be sold to you does not have adjustable damping - walk away (unless you never carry a pillion and never go touring and like the standard damping of course) Taking my R100 as an example - the normal load is me at a little under 130kg, but I sometimes have a Pillion and whilst her weight is a State Secret I operate on the theory that 70kg is probably right. finally If we go touring there are two panniers and a top box that swallow about 30kg worth of "stuff". so I need a spring range that is correct for me with no preload and can be preloaded up to allow for an extra 100kg of load.
The damping that is correct for 130kg will be like a pogo stick with 230kg - alternatively, damping that works for 230kg will be like riding a wooden horse at 130kg.
How to set correct spring rates? I am a little old school and I want to see about 1" sag when I sit on the bike, no more and no less, remember that you do not have all that much travel to play with as every inch of sag is an inch of travel lost.
How to set damping.
If it feels like a pogo stick - too little
if going over a wet white line launches your butt off the seat - too much
If it feels like a dead plank of wood with no transmission of road shock - just right.
Some really sophisticated shocks have adjustable compression damping as well as adjustable rebound damping, my own view is that this does introduce needless complexity (unless of course you are trying to tune things just right to get round a particular corner a mph or two quicker - but the theory of set up remains the same.
