I used a 8.8 M6X10 bolt with M6 washer and 242 (blue medium strength)
LocTite. The brass nipples unscrew counterclockwise.
The 10mm bolt was just below the surface on one intake and just above on the other by a few thou. A M6X8 would be better or file a touch off an M6X10.
Vacuum caps crack over time and introduce a difficult to troubleshoot wandering idle.
These are the bolts Tip and Katoum referred to.