Lucas is crap, it actually makes your oil less lubriss.
There have been tons of studies done and they all agree, if you use a decent oil to begin with no additives are neccesary and using them is actually harmfull.
I run amsoil 15-40 in my truck using a by-pass filter. With over 900k I'm burning less than a gallon of oil in 15k miles.
According to amsoil, the best oils for wear protection are a milspec # I can't remebr but you can only get it in 50 gallon drums. Then amsoil, then regular delvac, then royal purple, the stuf you're running is at the bottom of the list according to their study.
You'd probly be better off to swith to delvac.
I do extended drains prior to about 60k miles ago the Amsoil I was running had over 500k miles on it. I had to dump it because it got contaminated.
Lucas Oil stabiliser, just raises viscosity. Which if your engine is 'inspec' isn't neccesry anyway. With modern enginering standsrds and tighter bearing tolerances you want lighter oil not heavy oil. Hence the multiviscosity numbers. 15-40, means its actually 15 viscousity, but it protects like the old 40 wieght.
Its a confusing mess. But if you want to extend your engine life drop the additives and switch oils to either delvac or Amsoil. And then add either a Gulf Coast filter, TA installs them now in many plces, or get the AmsOil bypass filter. The "Gulf Coast" system is probly the best for running extended drains because everytime you change the bypass filter you'll have to add 1 gallon of oil. Which helps freshen you additive package. Also 'GUlf COast' has an oil monitoring program so if you send in your samples they'll call you and let you know if your having an issue.