I'm not sure if the '69s are different but my "old school" mechanic changed my rear main last fall without taking the engine out or removing the flywheel. went smoothly and no leaks.
What seal was put back in ? A rope seal really needs to be packed in the groove in the block and cap to be seated correctly. A lip type seal needs to have a sealant used or it will eventually spin. Also both type seals need to be trimmed perfectly.
