Remember that first ERF demo tractive unit, the one on the front of all the brochures and on the stand at the Brussels show in Jan '73? The one with no roof vent and no water filler cap?
I reckon I’ve worked out which unit it became. Although MMG 777P had no vent either, it did have a water filler cap. The only unit we have with neither, is HMO 220N (Estra/Calor) - the one that became Q824 RGC (wrecker).


All the other known NGCs had the vent and cap. If this demo unit was held at ERF in Sandbach for a couple of years it easily explains why it didn’t emerge onto the market unit 1975 on an N-plate, especially if it was the prototype.
It was earlier suggested on this thread that this unit became AFU 615 in Belgium (No.28 later 31) in the Van Steenbergen fleet, but it is difficult to imagine why, when that vehicle had both vent and cap.

A couple of years ago, ‘ERF’ of Peterboro’ kindly furnished with this info from the archives:
7MW
The first 7MW tilt cabbed ERF was chassis 22993, a model NGC 420 - A6.4.CU335 tractor unit. Recorded as a ‘Show Vehicle’. Despatched ex Sun Works on the 1st October 1973 as a stock vehicle to ‘■■■■■■■ Distributor Belgium’ 623/629 Chausses de Haecht, Brussels 3, Belgium. This vehicle was subject to warranty claims for defects found on delivery, and on nine occasions subsequently, the last being the 10th March 1976.
The second 7MW was chassis 24684, a model NGC 420 - A6.4.CU335 LWB. 15’ 9" wheelbase. Despatched the 14th August 1973. Again recorded as a ‘Show Vehicle’ to the same distributor as above. Note the date - we can conclude that this was the first 7MW to actually leave the works.
It was inferred from this info that because we knew the Thibaut drawbar outfit to have chassis 24684, that the other one must be the unit sent to Van Steenbergen - a fair assumption. However, we do not know how many ‘show’ vehicles ERF had in toto, nor how many NGCs they had in stock. But it is quite possible, if not probable, that the unit that went to Arendonk two whole months later, was not the unit displayed on the stand in Brussels.
With regard to the Calor tanker unit: I’m aware that we discussed that it would need to have its roof vent sealed of to meet pet-regs, but perhaps it was the other way round. IE, the unit fitted the bill because it didn’t have one. In any case, that could be sealed off without removing the vent itself. And it’s too much of a coincidence that the filler cap is absent.
Robert