Hello George,
I assumed this is a 901-903 Sprinter !!
Is this a 903 Sprinter or a Later 906 ?
I.E chassis number WDB 903......
Or WDB 906......

I may have been a bit hasty (Sorry) with the "No" to the electric tank pump as none of our 903 fleet Sprinters have them,(Only 2 wires to fuel tank sender) but looking on wis data it appears that some do (4 wires to tank sender unit)

Either way I would still go with the Fuel Filter first.

If its a 901-903 Sprinter it would be easier to remove top section of inlet manifold to do a continuity test on the glowplugs,(its really no Biggy to do) because you have to remove N/S headlamp and some grill and trim under the headlight to get to the glowplug relay.

Ian.