I would switch to a hi-miles synthetic oil. BTW Costco has a killer deal on synth oil right now if you happen to have a membership. 12 qt for around $22. Hi-miles oils have additives that can soften rubber seals and some gaskets, to help them seal better. You never know, it might even stop your leak!
You can use a thinner oil to help flush out the small oil passages in the hydraulic valve lash adjusters (HLA's). They tend to varnish-up over time and this will cause some ticking. But you're in Phoenix so Zero weight would be OK with a cold engine, but if you were to use, say, 0W-20 the oil has an max temperature range of 59 Deg F. You could safely use 0W-30 in Phoenix up to 86 deg F.
You can also add some Seafoam carbon-cleaning additive to the oil, 1 oz. per quart of oil. It's good stuff and won't hurt your engine. https://seafoamworks.com/knowledge-base ... am-in-oil/
Available at Walmart, NAPA, most other auto parts stores.
Isuzu actually put out a TSB about lifter noise, and their initial step was to refill with Mobil 1 0W-30 and run the engine at 2500 rpm for 30 minutes to help clean the lifters and purge air out of them. The TSB had additional steps all the way up to replacing the HLA's if the flush/purge wasn't successful.
What I'd do is run the engine with 0W-30 and Seafoam for at least 500 miles. Not gonna hurt it. I stumbled across an old post where they were using 0W-30 Castrol Syntex in their 3.2 all the time and it was very happy with it. Keep an eye on your oil pressure and as long as it's no alarmingly low, you're ok.
Anyway, if the oil/Seafoam is gonna work, you should know within 500-1000 miles. Then I'd change it out regardless, including new filter.
Far as oil leaks go, you can get some of the fluorescent dye that can be added to the oil. An inexpensive UV light reveals the offending leaky area. https://www.walmart.com/ip/1-OZ-UV-DYE- ... S/47907691
BTW a slight ticking from the fuel injectors wouldn't be unusual.
Noises that come-and-go are usually something engine-oil-related, though.
One other area for some nasty noises on these engines is the hydraulic belt tensioner. When they go bad, they can slap around, metal-on-metal, and it can sound just like a rod knock. And it does sound really nasty, not just a "tick". So maybe not what yours is doing at this time.
I have a copy of the ZuZu TSB if you'd like it; just drop me a P.M. with your email address and I can sent it to you; the site doesn't allow posting of .pdf files.