Lucas oil conditioner/stabiliser?

[Tazling]

Engine Oil Stop Leak – Lucas Oil Products, Inc. – Keep That Engine Alive!

www.lucasoil.com

I saw 4 litre jugs of this product line in my local parts store -- it claims it can reduce smoking in old diesel engines, and my 1968 (?) FL-120 is definitely an Old Smokey so I was tempted.

But it sounds a bit like snake oil -- too good to be true? -- so I was wondering if anyone else has tried it. Is it just another scam, or is there anything to it?

 

[Lepke]

My guess is that it adds heavy oil and an additive to soften the seals. If they still sell it, you could do as much with a can of STP. The theory is thicker oil will not get by the rings as easily.
Your engine smokes because oil is getting by the rings. Maybe, but not as likely oil is getting by the valve guides. If the smoke is black it could be a bad injector allowing too much fuel.