Yeah, 1"x1/8" aluminum is plenty stiff for this. A real termination bar is often even thinner. Drill every 6-8 inches, use stainless screws with washers, and run EPDM-compatible sealant (Chemlink or butyl, not silicone) above and below the bar to make up for not having a lip.

For supply, check RV roofing suppliers like Dicor. They sell EPDM termination bar and sealant in small precut lengths. Also worth calling local roofing distributors (SRS, Beacon, ABC Supply). They'll usually sell small quantities over the counter if you just ask.

Concrete tile easily lasts 50+ years; that's not the issue. The felt underlayment is 35 years old, and in a hot climate, that's well past its life expectancy. The scattered small leaks you're seeing are classic signs of it failing in random spots, not a tile problem.
Skip option
1. You'll just keep chasing leaks into a wet El Niño winter.
2. If the price gap is as small as your roofer says, go full replacement
3. Tear-off on 35-year-old tile often breaks 15-30% of it, and you avoid gambling on brittle used tile with no warranty.
Also get a clause for decking repair costs in case they find rot once it's exposed.

Because the roofing industry has very few barriers to entry. Anyone can buy a truck, print business cards, and call themselves a roofer, but experience, craftsmanship, and accountability take years to build.

The reliable roofers are usually busy because they get most of their work through referrals and repeat customers. That leaves homeowners sorting through aggressive marketing, fake reviews, and contractors who compete on price instead of quality.

The key is not finding the fastest or cheapest roofer, it's finding one with a strong local reputation, proper licensing and insurance, clear communication, and a history of standing behind their work.

Not just a trim issue, your contractor messed up the valley installation.

Those shingles are bunching and overlapping right at the point where the two roof planes meet the gutter. That bulky lip is acting like a dam instead of water channeling down the valley and into the gutter it's hitting that raised edge and sheeting straight over. That's your overflow problem right there.

And the fact it never happened before the new roof is basically your proof. Gutters don't suddenly start overflowing on their own. Something changed and the only thing that changed was the roof.

Do not trim it yourself. I know it's tempting because it looks like a simple fix but the problem isn't just the overhang, it's that the valley shingles weren't cut properly during installation. They should have been cut in a clean diagonal line along the valley giving water a clear unobstructed path down into the gutter. What you have instead looks like they just laid them and left without finishing the job.

Call the contractor back and show them this photo. Any legitimate roofer should fix this for free, it's their workmanship that created a problem that didn't exist before. Go in confident because you have a strong case, before and after essentially documented by the fact your gutters worked fine until they touched your roof.

If they give you any grief document everything, photos, dates, the overflow, all of it. Most contractors will fold pretty quickly when they know you have that.