What year is it?

The valve guide seals go bad as well and yes the plastic timing guides break do to age and not mileage....both jobs together can run 8-10K retail.

Google valve steam seals bmw 4.8 and there is a guy with a how to vid that sells a kit to replace them without removing the heads.

The 4.4 4.6 and 4.8 E53 when they get older are not really cost effective to own. Only if you can work on them yourself and know what your doing. Not many here can do the timing chain due to the vanos procedure on the cams...extremely difficult. I had mine done on my 4.4 with a shop foreman on the weekend and he even had to do it twice.

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2002 X5 4.4i Sport Wheels
2014 X5 35i M Appearance & suspension package
1995 Porsche 993
1972 Porsche 914-6
2020 GLE 450 Twin Turbo
2019 Alfa Stelvio 500hp Quadrifogilo
Many motorcycles