Jonathan,
I would try forced displacement analysis. This converges more easily, and yes, you can create a reaction force measure that tracks the force you need to apply. LDA+contact+enforced displacement can't start with a deformed geometry. You will need to start fom an "un-assembled" state and enforce displacements so that you finally reach the positions of your stiff components that you desire, and this will hopefully include the deformed state of your flexible seal.
Here's a picture where I have used plasticity+LDA+enforced displacement to find the collapse load for a 2-memeber truss-structure. I apply the load at the top of the structure through an enforced displacement constraint. As the enforced displacement increases, the reaction force first increases until it reaches the collapse load of about 9500 N. As the displacement increases beyond this, the force drops as the structure collapses. This would be difficult to detect had the load been applied as an increasing load. The solver can't converge once the collapse load is reached and you try to increase the force further.
This was a quick'n dirty example I set up for educational purposes, so mesh/time-step is somewhat crude.
And as you probably know, contacts are frictionless, you can look up the contact force, and multiply with coefficient of friction to get an estimate of the tangential forces.
/Mats L/
