In my experience with the 603 engine, I map out cylinde rhead repairs with the following plans:

a. oil leakage from/around cylinder head, including poor oil pressure to one particular tappet> usually a head gasket

b. excessive cooling system pressure> I assume its a cracked head, and then if I am able to verfiy after removal that the head is ok, then I celebrate.

9 times out of 10, the heads are cracked.

the exceptions tend to be very late #20/23 heads- these seem very storng and wer eused on late 603.971 motors [S350]

__________________
Pierre Hedary 1985 280SEL, 1970 111.026 in progress
Mercedes technical advice hotline: 407 765 2867
[servicing older Mercedes in the state of Florida with competence and passion].

From the standpoint of an honest MB technician, Vegetable oil is a threat to your diesel engine's mechanical integrity.