You can do better than linguistics and speech pathology. Please cite specific examples. You've read from quite a few of us already in this very thread that many of us can differentiate between milk and beer, so I am not alone in this thinking. There is a VAST difference between you, as a hearing person, idealizing what it is like to lipread, than a deaf person HAVING to lipread and picking out certain lip/tongue movements to make words clear. 38 years of being deaf and lipreading will do this for you, believe me. So think about that before you spout off on what words are distinguishable and what is not. Again, it is subjective to everyone. Having said that, this person (my roommate) that I did this test with is someone that just moved in, I've barely spoken with him so I didn't have a lot of previous experience conversing with him, so he was a good subject to try this out with. You've already read in some of my previous posts in other threads that I have minimal hearing and no speech discrimination - I could barely hear his voice and not enough to pick out words or even phonemes (sp?) to know which word he said.
And, to answer your initial question, the "L" has a distinctive movement of the tongue. Get in front of the mirror and say milk. You should clearly be able to see the "L" on your tongue and lips -- I've got 38 years' experience lipreading these letters. Others on this forum have said the same thing about the L. And, the "R" is slightly pursed on the lips whereas the "k" is not -- in "milk" -- so it was extremely easy to see that the word "beer" ended in an "R".