i have a RS turbo viscus Limited slip diff in a front wheel drive Fiesta, which while working when rotating the wheels when jacked up doesnt appear to do much when out on track, believe the viscus fluid can become weak loosing LSD effectiveness, is there anything that can be done with them? or a throw away item, just dont fancy £600 on a new gear LSD as need to strip gearbox anyway as now stuck in 3rd gear

Try Gearboxman, BARA Motorsports, DOME Motorsports and a few more who will all rebuild the viscous cartridge, from couple hundred quid

My dad can do this. We have same diff in my race car. He can make them as stiff or as lose as you want