Your Microdol-X soup should be at 75 degrees, not 68, when diluted 1:3. This is per Stephen Anchell and Bill Troop's book, wherein they recommend processing it for 13 minutes at this ratio and this temperature. A pro photographer I know told me to develop it for 18, not 13, minutes based on these factors. His full statement is as follows:

"For some time I searched for a developer for Tri-X film that was soft enough in the highlights so that they didn't block with full development. The old standby, D-76, even in its diluted form, blocked the highlights more than I wanted. I found my softer developer in Microdol-X about twenty years ago. With Tri-X I use it diluted 1:3 for the additional compensating action in the shadow areas. My development times are long, usually 18 minutes at 74 degrees, but I get a full ISO 400 and the negatives will show detail in brilliant snow or in a burned-in overexposed flash foreground light on down to the proverbial black cat in coalbin shadows."

I have gotten beautiful results with his recommendation above with my Leica lenses. I highly suggest you try this development technique, too. Remember, though, that the star effect you mention can be partly produced by the lenses you use--the quality of their glass and coatings. My Leica lenses do not produce flare at all. Whose lenses have you been using?