K engines generally want something like 20W50, or maybe 10W40.. the hydraulic lifters of 5 and 7K may want something different tho..
I would have thought 30 would be a bit thin? sure it will slightly reduce friction at sustained high rpm.. but you're not revving to 8grand?
if it is noise in 4th and 5th gear, under load at low rpm. are you sure it's not just pinging?
why not try a cheap 10W40 next, see how it goes, then a cheap 20W50 and see the difference..
K motors are not exactly high tech, and I can't why you'd want a 5W in there... the oil warms up quick enough, and then you are well away from the cold viscosity..
which lifter treatment and what is in it? is it just cleaners and viscosity modifier?
maybe the lifters are just stuffed?
should be reasonably easy to get them out after pulling off the rocker cover...
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