it is very hard as the cam bolt covers the key completely. If you take the cam bolt and washer off it may allow you to see without taking the cog itself off.
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)