Vanos bolts and vanos hub.
The tabs on the hub can break. I think turner or vac has hubs with thicker tabs, but the hub from turbotoy is the best:
http://www.tt-hub.com/
Its made from C300 steel, which is a very very exotic type of steel, normally only found in aircraft (the vac vanos hub is made from 'ordinairy' tool steel (4340))
That vac oil pump upgrade kit, is that only the upgrade for the chainsprocket or do you get a complete new/refurbished oil pump?
The s54 oil pump also has an internal piston (to control the oil pressure) that is prone to wear. See my post here:
https://www.zpost.com/forums/showpos...8&postcount=50
Also the chain guards on the s54 are an attention item. But thats I think also quite a job because you have to remove the timing chain cover.
You can also replace the timing chain tensioner, but I think that that issue is a bit exaggerated.