If Gulzar used PAG oil in an R12 system, He literally set your cash on fire, Secondly the charge is 900 grams not a kg - overcharging 100 grams can cause overload and loss of cooling.
thirdly - the expansion valve will clog with the wrong gas/oil mix - PAG oil is not miscible in R12.
finally - your static pressure cannot be 120 bar as that equals to 1740 psi.
furthermore - you are hiring useless people for work - working on the cabin AC of a 80 series cruiser is exactly like working on a 100 series corolla, the only difference being a larger system, If someone is charging you 3x the price of a corolla job - they are ripping you off.
btw - are all AC systems working on your truck or just the front unit failed?