oil pressure light

hi, just been reading the thread bout the guy (sorry 4got the name!) with the low oil pressure in his 200tdi, my 300 tdi disco has a similar problem, after driving for some distance (when the engine gets hot) the oil comes on at idle, but then goes out with the slightest touch on the accelerater. i have got a new pressure sensor to put on but just wanted some advice as to whether how serious this sounds? i have read things about it possibly being the crankshaft journals, big end shells wearing etc. just to fill you in, i recently had to fit 2 new conrods, when i did this i also changed all the piston rings and the big end shell bearings (but only on the two conrods i replaced) i havent done more than maybe 150 miles since then.