Do you guys know if it is advantageous for counter spring life to store the head in a specific position while not in use?
Like Ian, I have found that keeping the enlarger head down all the way with the D5-XL increases the chance of the spring breaking. Usually the band breaks inside the casing. I keep ours at about the 50 mark...a little less than halfway up. One of our instructors wanted me to keep the enlargers low so that shorter students would have an easier time using them (she was short, too). But we started to break CBSs right and left -- and this was when they were still readily available at $25 each!
I never had a counterbalance spring break on the Beseler 23C's. Way too hefty of a spring to ever break. We have 8 of these enlargers and I have had no spring break in over 20 years.
The counterbalance springs (CBS) are designed to hold a certain weight -- too strong and the head will rise, too weak and the head will fall. The D5-XL's are designed to hold 14 pounds each (two CBSs per enlarger). Until I could find some CBSs, I ran two of the D5's with only one spring each. A bit of a hassle, but the hold-down screws could keep them in place -- but they would not hold at a height without the screws.
Harry, the expert Omega guy, did recommend spraying WD-40 inside the CBS to keep it young and healthy. So that and keeping the enlargers stored at mid-height, should keep the CBS from breaking. I would not worry about using the enlarger at its lowest height, but I just would not store it there. But I now have 6 CBSs in stock (2 here, 4 on the way) not including the two I just installed, so I should be covered for a long time.
Vaughn