The rear right suspension doesn't seem to be automatically updated with the workshop installer. To fix it:

* Install the mod using the workshop installer

* Navigate to where the game is installed. For me, it's "C:\Program Files (x86)\Steam\steamapps\common\Street Legal Racing Redline"

* Navigate to ".\parts\MrSir_Running_Gear\scripts\RR_susp"

* Delete the "MrSir_RR_trailingarm_2.class" file

* Launch the game

* Either start a new game, or load a save without MrSir suspension installed on the car

* Open the parts catalog

* Navigate to where the suspensions are located

This should reload the part and update with the fix.