I have used both fluids, without any major problem. I would however not recommend mixing them. I replace my antifreeze every 30000 or 2years religiously. I believe you will find alot of discussion on this board if you do a search. Hopefully it will put your mind at ease.
m

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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)