In previous posts (at this link, at this link, and at this link), I had written something about the reliability of the Crusader tank, and the other cruiser tanks used in the desert. I have now come across a letter to the Brigade commander of 22 Armoured Brigade, presumably a response from an office in Cairo to what might have been a complaint about the mechanical reliability of the Cruiser tanks. It is reproduced below:
To:- Bde Commander, 22 Armd Bde
From:- B.O.M.E. 
4 Jan 42
The reason for the large number of cruiser tank casualties due to mechanical troubles in the last battle and approach march was undoubtedly due to the fact that 90% of the tanks have exceeded the designed mileage before a complete overhaul becomes necessary. This overhaul mileage was assessed at 1200 miles and prior to the last battle most of our tanks had exceeded 1200 miles and many 1500.
The above fact reacted in two ways. First, there was a large scale failure of water pumps, air compressors, and main fan drive sprockets due to wear or length of service. Secondly, owing to inadequate supply of new parts for the above assemblies, “cannibalisation” was carried out among parts which although at the time still function had already performed as many hours of service as the parts they replaced.
This method could only afford temporary relief and obviously in the case of tanks still operating with the Brigade fitted with such parts, no estimate of remaining life can be given with any degree of confidence.
Furthermore, at this stage, it is doubtful if fitting new water pumps assemblies etc., will appreciably lengthen the present life of the tank as cases are occurring more frequently of tanks becoming Z casualties repeatedly with different fault on each occasion.
 Presume this to be ‘Bureau of Ordnance, Middle East’, but happy to be corrected
 The ‘last battle’ was the battle between Christmas and New Year in the Uadi al Faregh, in which 22 Armoured Brigade received a savage beating at the hands of the Axis forces, and the approach march therefore must refer to the march of 22 Armoured Brigade from the re-organisation area south of Gabr Saleh, where new tanks were drawn, to the operational area south of Agedabia. As the crow flies, this is at least 400km, and in reality considerably more.
 Puts the service interval on my A4 in perspective. Although it too has coolant pump issues!
 Royal Army Ordnance Corps – the branch of the British army dealing with keeping stuff functioning (there was a reorganisation in 1942).