My civic hasn’t had the transmission fluid changed in ages but it still shifts well. It has 124,000 miles. Would it be safe to add prolong or lucas trans fix to see if I could make it last longer? Or just leave it how it is.

 

I'd gradually get back to a schedule of a drain and fill only (no flushing) of Honda DW-1 ATF every second oil change. Owner's manual recommends every 30K miles I believe at the most.

 

Don't use any additives. Honda used to make the best auto trannies and they are bullet-proof if maintained well. Just follow NDNV's advice and you'll be golden.

 

I’ve been doing as advised This is the one transmission that is crap tho