Someone I came across recently left their mini running for the duration of the event - even while parked for 2 hrs. He said he has a hard time starting it because they were designed to run on leased gas and because of running so much unleaded through it he had sunken the valves way too far down in the soft seats. I watched him add a bottle of lead additive to it. Is this something I shipbuilding be doing or be concerned about?
No and no. Over a LONG period of time it will pit and cause smoking, at which time you convert the seats to unleaded if you feel so inclined.
Thanks. I wondered why I would want to add lead additive if it seemed to run fine on unleaded. What would be his reasoning?
For your friend it's too late - if he can't get it started it's because the clearance on the valves is gone from the valves receding into the seats - he needs to pull the head and have hardened seats installed and a valve job done.
For you, the best indicator is if you have to keep adjusting your valves - especially the exhausts - because they're tight - that's the telltale. If you're not doing this already you probably don't need to worry about it.
Later cars supposedly had hardened seats from the factory, but I hear mixed opinions about this. However, if the car has many miles on it there will already be a decent amount of lead built up on the seats already, so no more is needed.
The best way to make sure you never have this problem is either to never drive your car or have the hardened seats installed.
When I did my 5100 mile trip I had to adjust the valves every two days. Had hardened seats put in after I got back. I was not using an additive because I though I already had the hard seats.