Hello,
Rutland District Council had at least two of these Mack NM6's operating around the county until the late 1970's.
They were taken over by Leicestershire County Council, and were kept in a depot at Croft.
In about 1989 one was still there with an FP number plate. You could still see the Rutland County Council coat of arms under the layers of yellow paint.
I was told that it was still operable, and was in fact invaluable on the steep section of M1 going up past Leicester and Charnwood, because the modern Foden gritters didn't have low enough gear ratios, and once they had to stop on the gradients, they couldn't get re started on the ice and snow.
The Mack's could crawl their way up the worst of the slopes, and steer around stationary trucks, going on the verge if necessary.
The only complaint was the fact they had no heaters to speak off.
Regards
Nick Balmer