We have 4 vehicles with over 100K and one that probably has around 300K but the od hasn’t worked for many years. We put Slick 50 in everything when it gets past 50K.
My husband is bad, we change the oil every year or if we are going on a long trip. We’ve never had to replace an engine.
I let the guys at Jiffy Lube take care of the oil, just not worth the time, and they put in the 'older vehicle' oil. I asked them what the difference was and was told that it was the equivalent of putting a quart of slick 50 in it.
You sound lucky.Owners manuals suggest 7,500 miles, and while the oils today are far superior, I change it around every 4,000 miles, to remove particles and dirt, that sort of thing. I guess that you are not putting too many miles on them (between changes).