OK...so it's a NORCOLD ---not a Dometic
That is the 'selector switch and SAFETY Valve' that is binding
Part of the 'combination control'
Combination Control is NON-SERVICEABLE (can not be repaired/rebuilt etc.) and must be replaced when it fails
Good news........some are still available
Bad news........roughly $320 PLUS
BUT......BUT there could be light at end of tunnel
That combination control went thru a RECALL (defective rubber seal)
for units built Jan 1987 thru May 1995
Your 1992 falls within the recall period so if never done you may be able to get one from Norcold
Good info..descriptions etc
Service ManualCombination Control part Number---------- Norcold 624274
Recall Info