FX4 taxi. If you can find one still being used ask the driver where he gets it serviced. You can bet it’ll be a grubby back street place where they’ll likely have a couple on a shelf
I don’t know about an S2 but I purchased an FX4 taxis heater for my S4. However there are some differences. The matrix is the same but the box inlet and outlet pipe positions are different so needs minor modification.