Seems Ã–hlins typically specifies '2.5' viscosity.
I call 'em "dampers" but to each his own.
There are other thicknesses from which to choose as well.
Are those Tractive built Xida's in the last photo? I've had the pleasure of autocrossing a vehicle equipped with them. Crazy how they can turn a fast sweeper with a number of dips and rises into a fast sweeper that doesn't require a second thought.
Most race teams have shock dyno's in house nowadays. Those same drawers of metering and repair parts utilized for the different shock/damper manufacturer. Nothing like going onto good ol' boy Bubba's World of Outlaw's hauler and seeing some dude rebuilding/remetering and dynoing some shocks. It's not as if there aren't already a couple dozen sets ready to go in drawers. I prefer this stuff because it's a pretty blue color.
We freshen our off road toys shocks/dampers often. Change valve stacks around a little bit if needed, but they are toys, not competitive racers. We usually use Amsoil, works good and a guy down the road has in stock.
Those are like a suspension fork or shock on a pushbike or motorbike - rebuildable and you can tweak it unlike a sealed shock.
I've seen a bike mechanic friend rebuild a $1000+ Fox mountain bike fork and a long time ago I saw a KYB or Showa motorcycle fork pulled apart, cleaned and checked for straightness against a dial gauge on a slab of marble. After that, fresh oil and new seals before it was put back together and repressurized to spec.
On pushbikes, SRAM and Fox want you send it into them or QBP(the biggest bicycle parts wholesaler in the US) for service. Cleanliness matters on these.