Here is a critical little oring that is hard to find and hardly ever gets replaced. There are two of these located on the end of the oil filter cap shaft on 1977 to 1985 4 and 5 cylinder diesel engines (expcept 190D). These do get hard and brittle with age and in some cases will just break off. Fluctuations in oil pressure may be an indication that these o-ring seals are bad. They will last through several oil changes so replacing them every year should be more than adequate. This kit comes with four (4) o-rings.
NOTE: This one is so easy instructions not required....
Applicable oil filter housing cap