On the majority of Healeys that I have been working on I have found a couple of important imperfections and faults regarding the oil feed to the rocker pedestal.
The first imperfection is that the factory used a very fine thread for the oil feed banjo bolt and the hole in the pedestal. If someone tightens the banjo bolt too hard it is very easy to strip the threads out of the hole in the pedestal, since it´s made out of aluminium.
The second fault is that owners/mechanics has assembled the rocker gear on to the head before they mounted the banjo bolt in it´s place on the pedestal. There is a hole in the rocker shaft that shall be perfectly aligned with the the threaded hole in the pedestal. If the rocker gear is mounted to the head without first screwing the banjo bolt in place so that it engages the hole in the rocker shaft, thus aligning the two holes, it is very easy to get them misaligned. When one then tries to screw in the banjo bolt it will strip the threads in the pedestal, due to the resistance from the misaligned hole in the shaft. Once this has happened, which is the case on many Healey engines, the joint between the oil feed pipe, the pedestal and the banjo will not be thight, resulting in lost oil pressure for the rockers and shaft. I suspect that this might be one big reason for the common problem with worn Healey rocker shafts.
One good remedy for
this problem is to make a new banjo bolt with 3/8" UNF thrads and to mount
a helicoil thread of the same size into the rocker pedestal.
The second remedy regardless if you are using the original bolt or not is to always fit the banjo to the pedestal before mounting the rocker gear. The banjo can then easily be removed in order to fit the oil pipe. Always fit the banjo bolt to the pedestal before mounting the rocker gear to the head.