More a pushing of the valve toward the front than a twist, which will put the tubes into a bind. Twist the valve along the axis of the line out (the one you are trying to remove) while pulling on the line toward the back of the car - like removing a baked on vacuum hose. Penetrant on both lines and put some ass into it.
(If you DO get it off some high temp anti sieze may help future maintenance) apply sparingly to avoid getting it into the tubes!
Oh and putting it back on is at least twice as hard as removal!!
RIP "Betsy" (Oo=*=oO)
'96 E 3 2 0 (W 2 1 0) M 1 0 4 (Totalled)
Spaces in sig so as not to screw up the SEARCH; every time someone searches for that MB they don't want my sig!
2004 Audi A8L
'98 VW Passat 1.8T 5M
'87 Alfa Romeo Milano 2.5L 5M
'67 Impala convertible, 327cid