The non-functioning Horizontal L4-C L41659 on Pier2(SW) was replaced with L41366.  While at it I 'leveled' the L4-C based on its clamping bracket D030586 but other data suggest that may only possibly help.  This required about 0.09" of shim although this isn't the amount of out-of-level due to geometry.
I've left the HEPI system on WHAM3 unlocked; I want to see if there is any slow creep of the system while free.  I'll lock it up in the morning and then summarize the numbers--yes there were some shifts from locked HEPI to unlocked position.