I would change out the rubber it is easy and it does get brittle with age. I would replace all the rubber on mine, I did it with the injectors. But I don't think that is your problem. Is the high idle at P or in D or both.
m

__________________
Martin Ingram
Colorado Springs
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)