Using the Lucas is the cheapest and easiest way to diagnose the problem without having to tear down the vehicle. If the problem is the front bearing on the input shaft of the transmission (which have been known to give trouble) then a clutch and pressure plate assembly won't do any good. If it turns out to actually be the throw-out bearing, the Lucas is good for your transmission anyway, especially if the transmission is high milage. If this vehicle is your daily driver, then doing this will isolate the problem to one area or the other, which will save you time (knowing exactly what to fix) when you do take it apart, and minimize down time on your vehicle. It does sound like the throw-out bearing, but if it is; the noise should stop when you mash the clutch. At any time. If you spend 8 dollars on a bottle of Lucas and it turns out to be the throw-out bearing: you've just done a good deed for your transmission. If you don't try the Lucas and it turns out to be the front bearing......then you get the joy of taking your truck apart again after spending all that money on the clutch and pressure plate.