Lead Additive

[june2017]

After doing quite a bit of research, I'm stumped on the use of lead additive in my '74 B. The previous owner did use it. He could not be sure if the owner before him, who had engine work done, hardened the valve seats. He thought it might have been done but we lack documentation.   So he ran it with lead additive at about 6 ounces to each full tank of gas. 
What do you advise? It's not daily driver and has about 118K miles on it.
Runs well but a bit rich.
Thanks for considering.
Mark Gallucci
Upstate New York

[JohnTwist]

Tetra-ethyl lead is illegal to sell.  Therefore it's not in any of the "lead" products.  At the end of leaded gasoline, the government, in its inestimable wisdom, allowed the fuel companies to label their phosphorus enhanced gasoline "leaded gasoline." 
My approach on this additive is that it is snake-oil.  I will listen to all those who make a case for using it, but most (90%+) owners do not use it.
Save your money! Eventually, someday, the a valve will fail and you'll need to perform a valve job.  At that time you can have hardened seats installed.
The savings from not using the "re-lead" will pay for the seats. 
There ARE octane enhancers -- for sure!  But those boil away in a short time (hours - days).  Those, too, are unnecessary in our MGs.
Oil with added ZDDP is, absolutely, critical.  The zinc will save your camshaft.
Hope this answers your question and allays your fears.
John Twist