A leak down test is no more invasive than changing sparkplugs. If the owner of a performance vehicle is hesitant to do this he is probably hiding something he does not want you to know about.
With respect to the
oil analysis, the use of what amounts to a test tube's worth of
oil from the engine for analysis should not create heartburn. If it does we are back again to the question of what it is the owner is attempting to hide and why.
Ed