@paul cain : Thanks for your suggestions. I'll have a check. SFDon also suggested a high temp version from Tesa for the engine compartment. I wonder what their chemical resistance is; i"ll see if i can dig up a spec sheet. .
Ordered some tesa 51036 high temp tape for the engine compartment. The spec sheet do not state anything on the chemical resistance, so I will give it some home tests with different solvents.
At least the Tesa 51036 tape is also a very good match to the original, compared to the coroplast.
The coroplast has just a tad more surface with short fibres, but it matches better in appearence as it has a weaving pattern that forms diamonds, like the original.
The original is a bit smoother then the coroplast, which is better matched by the Tesa, but the Tesa is a bit shiny and has lines running across it from the weaving instead of a diamond pattern.
In my pics the small roll is coroplast, the Large roll is Tesa 51036 high heat engine compartment compatible type.
Last pics next to a piece of original tape, still on my harness. Which was cleaned with solvent and dried.
I think if you put two cars next to each other, one with coroplast, the other with Tesa, I wouldn't be able to tell the difference. For me both pass my acceptance criteria, and I'll be using them both; coroplast as I already have ot for the interior, tesa 51036 for the engine comp harness.
In the end I think our blinkers don't really care about all of this....