[s-cars] cabin filter retrofit?

[Dave Forgie]

You wish.  Can be done but likely at a cost equal to the value of your car. 
Requires the swap to the later S6 AC box under the passenger side cowl.  
The 92-94 S4 boxes do not have the slot for the filter. The NA S6s came with 
the slot for the filter but typically, no filter.  In that case, all you need to do is
 add the filter.  For the S4s, bring a hanky and take Claritin. Cheaper and at 
least as effective. 

Dave F.