Maybe another problem, the Injection Pump??
Our '98 Tdi turns over slowly/sluggishly also on it's first start of the day, but it fires up in less than one rev of the crank.
I'm wondering if you may have the cold (first) start problem that I had on our first Tdi, an rough old '97, it was hard to start first start of the day due to the fuel pump having a fuel leak on the throttle shaft, exacerbated by parking on our driveway, nose uphill, just an "o" ring seal, once that was fixed it started the same as our current Tdi is starting.
So what I'm saying is that there may be a delay in the fuel reaching the injectors due to a small amount of air in the pump at the first start of the day, (the fuel drains back to the tank via the return line due to air ingress into the IP through the leaking "o" ring), then thereafter throughout the day there is an immediate start due to a full prime of the pump. It is a problem that seems to present as an electrical problem i.e. engine turning over too slow when cold. I tried all the usual remedies, Glow plugs, installed a second battery, checked all electricals, put a relay in the start circuit to the starter, all to no avail.
Check around the top of the Injection Pump near where the throttle cable connects to the lever for any sign of fresh diesel.
And how I proved the problem was overnight parked the Disco back end significantly uphill, or nose down with a full fuel tank, the vehicle started fist rev each time. After identifying the problem it was a simple and cheap fix to replace the "o"ring seal in the IP top cover.
Just a thought, but may help.
