I'm just about to buy a little project.
It's a 2004 4.4 vogue with 137k on it and the seller is saying that there's a rattle noise on start up and sometimes when the car is fully up to temperature.

Says it doesn't affect the car and shows no signs of any real issues on day to day driving and the timing chain guides etc were replaced in 2016.
Hes taken it to a garage and they have said there's two options which are replace the seals with a kit or replace the whole thing which is around a grand.

For anyone that's experienced this, does the repair kit generally work or am I basically just looking at a full overhaul?
(I realise this is a piece of string question)

The car has lpg and a few other goodies and I'm buying it for £1350 so am OK with it.

I have a 94 325i that I will be doing the VANOS on shortly. Asked Besian about the lifespan if the seal replacements. They have said no reports of them failing. The process is a bit different for the 4.4 and a bunch more wrenching. I'll do mine at next chain and guide replacement.
Before you go that route you might first change the solenoid check valves. Made mine much more tolerable. A whole lot cheaper and easier. You will need a 32mm? Socket with a thin wall. I got a cheap one and put it to the grinding wheel. Best to replace the solenoid seals too. Reassess after this and a fresh oil and filter change.

Thanks.

I'll have to look into that when it arrives then. Hopefully it's a cheap (ish) fix.

I have 165k on mine. There is always a little VANOS rattle on first start up. I imagine if it wasn't well maintained it could wear the vanos more but then I'd look at everything else.