Difference between S1 and S2 rear shocks

[Hachille]

Hello everyone
I am looking for rear shocks for my S1.
I had in place AVO PE 554 (Special Banks). But I don't like the quality of these AVOs and today they are losing oil.
I would like to switch to GAZ-SHOCKS as for the front axle.
Does anyone know the difference between S1 and S2 shocks? At "GAZ-SHOCKS" GP6-2149 or GP6-2155?
I don't change my springs.

[Hachille]

To give more information. Are the AVO P544 (Special Banks) with S1 or S2 dimensions?

[jbcollier]

S1 and early S2 front shocks have narrower spring seats than late S2 and up shocks.  There was all sorts of wackiness around headlight/ride height for US bound cars.

Other than that, I would have thought the shocks would otherwise be identical.