Pugsley,
Ahh that horizontal bar that isn't a horizontal bar LOL, all grills are the same on refurbished class 37, I've just gone through all my 400+ photos and all show one piece grills at either end. However and hopefully this will explain the perceived difference, the second man side is the end that has been modified, originally it was two half height grills. Nose grills are not end dependant but side dependant and thus mirror each other irrespective of end viewed.
When they were refurbished they left a horizontal bar across the opening, just like the drivers side which also has a full opening. However, the drives side is just a grill for ventilation, the second man side is the intake for the traction motor blowers. Over time the second man grills accumulate dirt from all the air and grit sucked in, however the area where the internal bar is accumulates less and thus retains its colour better and gives the impression of a horizontal bar.
Original nose end on drivers side showing dividing brace and pipework behind grill, 37 150.
Refurbished loco with internal bracing added like drivers side and showing fixings for internal filters to traction motor blowers, 37 418.
Effect of internal bracing on weathering at traction motor intake, 37 425
37 404 with weathering dividing bar at 2nd man side at far end and slight weathering on drivers side.
37 412 with weathered dividing bar more evident on one grill than the other.
The only odd one out that I can find is 37 425 which has a damaged grill at #1 end drivers side and was blanked out for many years.
Copyright exists with all original owners, images shown for indicative purposes only.
That's my understanding of the whole issue
Apologies to Tom for the digression.