I used heater hose for this and it works just fine. This is yet another example of a poorly designed $.50 part which makes a $$$ system unusable. When I bought my '88 560SL I spent hours debugging the ACC system, checking and changing parts until I discovered this little piece of foam all disintegrated behind the dash...literally 5 minutes later the ACC system was working as good as new after I stuck an 8" piece of heater hose in there.