I had an excellently productive evening.
I’ve been chasing an economy issue with this car for ages. Started using way more fuel (15L/100km, instead of the more usual 12L/100km) and it was proving impossible to hunt down.
Then I noticed the oil smelled somewhat like fuel - which made me instantly think I had a leaking injector. The car was also hard to start when it hadn’t been run in a while, which I felt was a lack of fuel pressure issue (the 740 only primes on cranking).
To fix this, I put an injector service kit on, but once I’d finished, I realised that that wouldn’t account for the behaviour I was seeing. The kit just fixes leaks at the fuel rail and the manifold mating surfaces, not internal leaks of the injector.
Regardless, I finished reassembling the fuel rail and tested it on the ground with a spare fuel pump. None of the injectors leaked under pressure; I wish I’d tried this before putting the kit on, in retrospect.
In any case the car now runs, so I haven’t completely destroyed anything by refurbing the injectors. I’m hoping that between this and installing a properly functional brake booster will solve my economy issues, through the injectors working better and the brakes not dragging. No idea if the brakes were dragging but in any case they shouldn’t be now.