You can use the Tamiya friction damper grease and there are three to choose:
soft 53174, medium 53175, hard 53176. These are pretty good and stay consistent for quite some time since they are designed for this application.

You can also use thick silicon gear diff oil in 30K to 1million range in most cases to achieve pretty good result. They will need to be rebuilt more often because these are newtonian fluid basically and despite being very viscus they flow out of the damper given enough time unlike the grease. But you can go in much finer increments in weight.

But from limited experience it is very hard to build these friction dampers very very consistently (compared to touring car style shocks). The amount of air in the damper really does change damping a lot. if you can do a good job making the air content consistent you will get a consistent damper. Grease is a little less sensitive than the oil but they are both affected.

In general the thicker the roll damper the lazier the car is until you really get into the too much over dampen range which will do the opposite. But from some experience that usually doesn't happen unless you go crazy stiff. 1.8 T bar is good for higher traction and should work for you. 102 is a decent carpet car but probably not the best out there. It is a great asphalt car though.