AEC never overcome the head gasket problem , so many failed that i know and mechanics could report yet another and get paid for some overtime sat in the pub , i still have some AEC head gaskets in my shed , the Leyland 400 and 370 could pull very heavy loads (20 ton) and never boil , the four -in-line had two axels and gave 11 ton combined when the single axel was 9 ton and total wid two axel tractor 20 ton , four in line was 24 ton as same as tandem bogie but three quarter ton lighter and all tyres conformed to road camber , so… equal loadings at all time ,tractor two axel 14 ton four in line 11 ton = 25 ton (leeway of 1 ton ) later single axel 10 ton and 24 total ,(even 32 ton wid three axel tractor possible) so no longer any need for four in line . DAF four in line the axels rotated ALL THE WAY so the punture was presented to the outside , easy and peasy .