Regarding Tufnol for gears, my Opel Kapitan had the large timing gear made of Tufnol. This broke 2 teeth 300 miles into the Northern Frontier District in Kenya and left me stranded. My companion hitch hiked back to Nairobi and brought his Rover 90 back and towed me all the way home.
I entrusted the repair to a local garage who did the job and I paid the money. 1 week later it happened again but this time within the area of the local AA so got a free tow in. This time I did the job myself and the new replacement was an Aluminium gear. Enquiries to the Opel spares dept. said that I was the first person to buy a gear for at least a year. This meant the local garage had used a part from a scrap engine and I went bald headed at the owner who then admitted using a'Used' spare and I got my money back. Ever since then I have mistrusted Tufnol gears.
The fault showed as the Cam shaft keeper yoke plate having come loose and allowing the cam shaft to push forwards due to the helical gear and the cam followers disintegrating and a piece getting into the gear train.
An interesting follow up then occured, I was talking to the German Opel engineer in house and stated that I could remove the camshaft without lifting the engine. There then followed a demonstration with him paying me 500EA Shillings on the Bet he made saying it was not possible.
The answer was to undo the right side engine mount and jack up that side of the engine and then remover the radiator which then allowed access to the camshaft and its removal. Previously they would charge over a 1000EA Shillings for the job which went to a 1hr. job from 3hrs.
Clive