I have a '92 300e and '88 260e that both make that noise sometimes. They have been doing it for years and it's not getting worse so I have not tried fixing it. As far as removing the rocker arms, it is very easy. Each cylinder has its own shaft and they can be removed one at a time without special tools.

I am curious if the hydraulic lifters are really the source of the noise. Please post a follow-up on what you discover.

John