I have a condition with my 2000 M Roadster (S52) of lifter/tappet ticking. It doesn't do it everytime I start the engine. It may or may nor tick when cold started and not do so after the engine is warm. Or, it may tick for a few warm starts. You never know when it will do so. The tick goes away as the engine warms. I changed the oil and use synthetic. I also use S-100 fuel additive. I'd appreciate any advice.