My '95 A6 has an intermittent (fixed delay) wiper and I've spotted a variable wiper stalk on ebay (from a later A4/A6 I think) - looks like an identical fit but want to know if this will work as is, with my existent relay?

It would make such a difference...

 

you can buy an "intermittent" relay -

VW or Audi dealers -- VAG P/N 1HM 955 531 A
The "A" is the important part, but this part has been superceded, so when you ask for it, they may try to give you a part that ends with "B", "C", etc. The "B" part does work, the "C" does NOT!

Just replace the wiper relay with this one....
Operation:
1. Turn the wiper switch to the intermittent position then turn it to off. The wiper will wipe once.
2. When you need the wiper to wipe again, you place the wiper switch to intermittent and leave it there. It will remember the time interval and repeat the wipe at this interval.
3. To change the interval, just turn to off (wiper will wipe) and then turn back to intermittent position to set the new time interval.
4. The relay is reset to a 6 second default interval when ignition is turned off.

A lot easier than replacing the stalk!