How to show related posts by custom taxonomy?

Hi,

I’ve been at this for hours and can’t find a straight answer. I’ve been through many, if not all, of the topics on this forum, and tried almost all of the popular solutions on the interwebs. But none seem to work.

I have a custom post type: ‘clipping’ as well as a custom taxonomy: ‘tag’. All I want to do is:

1: on single.php retrieve posts that contain one or more tags of the current post.
2: randomize and retrieve only 4 of all results.

I found this topic, which is now closed, that seems to do what I want, but not for a custom taxonomy.

I’ve also tried the following tutorials to no avail:
Justin Tadlock
Stack Overflow
WP forum thread

There’s many others I’ve tried that I can’t find the link to… hopefully someone can help me out and perhaps put an end to the search once and for all!