vw audi oil pressure?

av got an agin 1983 audi 100 with the vw 8valve engin in it the milo stoped at 16800 miles in 1998 so not sure of present milage it gets plenty of oil changes -always has ,but always wen startin up the oil presure light stays on about a second or two and the hydraulic tapits clatter ,as the light doesent flicker when hot can only asume presure is reasonable , apart from a rebuild and pump change can anyone sugest a quick fix untill next year wen il have more time on hands to sort it , like a thinner oil or athicker oil, like i said presure at temp aint a fault yet so i want to build pressure quicker. cheers lee