Attached is an original service bulletin from BMC. The text of the bulletin is as follows:
The Austin Division of British Motor Corporation recently issued Service Journal A/139 pertaining to the correct lubrication of the Laycock de Normanville overdrive as used on above roadsters. To underline the importance of this information, we are mailing you this bulletin of ours.
Always make sure only one of the 8 factory recommended oils of a viscosity of S.A.E. 30 is used and avoid mixing the gearbox lubricant with any kind of additive. On certain occasions we have observed a tendency to add, for instance, molybden containing special gear lubricants etc. to the transmission oil in attempts to reduce or eliminate gear noises. This procedure is not accepted by the car manufacturer.
Please be advised that such practice is not permissible with overdrive equipped Healeys and will only lead to you voiding the customers warranty. In view of above it is also suggested you take this standpoint in discussions with car owners should the topic of transmission lubricant additives crop up.
We strongly suggest you notify your lubricant personnel of this ruling so as to prevent the addition of any special additives to the straight engine oil which is recommended for the Austin Healey gearbox and overdrive. The gearbox and overdrive lubricant is identical and there is no separate overdrive oil, this oil being filled into one combined filler hole on the gearbox casing. However, there are two drain plugs, one in the gearbox casing and one in the overdrive housing. When topping up or changing the transmission oil cleanliness must be observed to avoid dirt and grit entering the unit and getting into the overdrive, where such foreign matter is likely to cause malfunctioning and defects.
The following engine oils are recommended for Austin Healey transmissions by the car manufacturer:
Dickhams's NOL Thirty
Energol SAE 30
Shell X-100 30
Filtrate Medium 30
Esso Extra Motor Oil 20W/30
Sternol WW 30
In cases where the above brands are not available the use of a recognized and well known brand (Standard RPM, Pennzoil, Valvoline, etc.) is permissible under condition that the correct oil specification is adhered to: Low or non-detergent engine oil of viscosity SAE 30. The use of not widely known and represented, low grade lubricants bust be avoided.
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