While I am not a fan of additives, most are border line snake oil and have way too many things in them. I have recently tried 2 things as a diagnostic test.

People try all kinds of snake oil to fix issue but sometimes it can actually help diagnose a problem. The trick is to do your research and do not expect miracles, my Disco had 2 issues a light sewing machine tick at idle once warmed up and what I felt was poor throttle response on hills at non hi way speeds.

Tried injector cleaner, some improvement in throttle but not much. Research lead me to O2's possibly being the the issue, so test 1 if you will.

Tried some catalytic converter cleaner. This will not fix a plugged cat ever What it can do however is clean your O2 sensors and improve performance and throttle response. This only works if you sensors have been somewhat compromised buy ,burning a bit of oil, some coolant from a head gasket leak, or over carboned from running very rich for along time.
In my case following the directions both improved my O2 sensor response and throttle response, very noticeably. It also indicated the my O2's are likely getting on and need to be replaced. I did not expect a miracle and did not get one, but I my Disco responds to much throttle better now and shifts better as as result to what I expect as normal. Buying me some time.

I still need to take the Disco to a muffler shop and have a back pressure test done to check the cats, before replacing the O2's

2nd is the Liquid moly hydraulic lifter cleaner, I have a light sewing machine tick, you can only hear standing beside the engine bay, you can not hear a thing inside even with windows down. Now my bet is rockers, I have a spare set but before I do that I want to eliminate sticky lifters which cause the same sound. The Liquid moly only does one thing, help clean small oil passages of the kind found in hydraulic lifters that can cause a sticky lifter. It is not heavy duty flush or clean that can cause problems, by dislodging sludge. It will not improve oil pressure.
This is a no loss for me it is all of $10.00 if the noise drops or best case goes away I know the cause of my tick, if not more to be done

I will report back on this after a couple of hundred K, or if there is a change before that. Once again this really only buys time if it fixes the issue as those lifters likely need to be replaced.

Why this route is simple if it is lifters the best fix is lifters, cam shaft and bearings, pushrods and rockers. And as I understand it I am not doing those bearings engine in place. So significant work, you want to know for sure that is the issue. You can replace just the lifters, pushrods, and rockers - BUT you have to know you camshaft is good and that can be tricky for a DIY guy.