I agree but my 98 did not use additives etc before I got it. I can show you Lexus slips since I need a new EGR put on the very next year since the engine has issues in this area. Just do a search and you can find out.
Also if Lexus designed my engine correctly there would be no issues with plugged Ivac, TB and intakes now would there......there would be no slow to accel, rough idel, low mpg.....
I can show you the new shirt I used to clean my TB and ivac after 80K miles. Yea, it looked realy clean. You could have used it to clean up tar and it would be the same color.
Here you go:
http://home.comcast.net/~94gsxr1100/lexus/tb_clean.jpg
Additives have there places and they do work. I had to replace my Radio LCd screen too. I wonder if the engineers where on a ITO break or something when the signoff came around.
All cars have issues. My wifes last Toyota had 200K and the 3rd owner just sold it. But what you do not know is all the $$$ it too get to that point. And that was maintained at the dealer and the dipstick still had varnish on it and leaked from 80K miles on....
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this still doesn't answer the question whether aftermarket additives prolong or shorten the life of the engine. After all, this your experience which may or may not be repeated by others. What is really needed is a very long, very expensive test running a set of cars as engineers intended and another set with aftermarket additives - both driven in absolutely same conditions. Only a few years later we might have more or less definitive answer. At this point, all there is a gimmick which appears to work for some ppl in the short run with unknown long-term consequences. After all, you can't really compare service record of engineer maintained vehicle with one subjected to aftermarket additives, 'cause both are different, used in different conditions, for different purposes, driven in different styles. Too many variables to account for, too little confidence in a meaningful comparison.
Just my $0.02 :)