Camshaft wear

From Citroen SM Wiki

The Citroen SM camshafts are classic 70's flat tappet cams which require special attention. Since the early 90's, due to EPA requirements, an important additive has been removed from all off the shelf oils available at your store, ZDDP. This additive was designed to protect the flat tappet cam, unfortunately, it shortens the life of catalytic converters. So the solution was to remove ZDDP from the oils since modern day engines use roller camshafts. The unsuspecting SM owner buying the best available synthetic oil will in fact be contributing to the demise of the camshaft lobes, unless a ZDDP additive is added to the synthetic oil. (See for further details.)