Does the manual transmission of the Navara still have the inherent design flaw of being easily damaged by water ingress?

Why is there no diesel version?

Why is there no diesel version?

I drove through some water, and now the clutch feels super heavy. [I need a moment]

Cars that go through water can take in water. There's a modification part called a snorkel, and once installed, it can prevent this. The rear axle also needs one since it's more prone to taking in water.