Is there any damage that a lens can have that is unrepairable?

Question

Just wondering after I dropped my lens and had it repaired is there any specific kind of damage that would ruin a lens to the point where you'd be better just buying another used one.

I'm specifically curious about mold, as I've heard stories of that destroying lens elements, but couldn't you just replace those elements?

I'm asking this question to help make decisions about cost effectiveness of preventive measures.

For exampe, if mold dmg can be easily repaired then I won't invest in a dehumidifier case for my lens.

Answer

Since lens replacement parts exist and there are people who know how to disassemble and assemble lenses you can say that theoretically there is no damage that can't be fixed -

However in the real world there are kinds of damage that the manufacturers won't fix and even more kinds of damage where the cost of fixing would be more than the cost of replacing the lens.

Everything below this line is second hand information because I've never personally sent a lens to be fixed, I don't guaranty this information is correct and I will gladly edit or remove this answer if someone that has more experience or official information answers.

• I've heard from multiple people who tried to get mold damage fixed and the companies just returned the lens as "can't fix", so I believe it's highly likely companies will not fix mold damage.

• I've also heard of cases where lens companies won't replace broken inner elements, I don't know if this is a general thing or specific to some lens models.

• And finally I've been told that the front element is always replaceable and that it's one of the cheapest things to fix in a lens - I've only heard this from one source (as part of a "why you shouldn't use a protective filter" speech) so I don't consider this information reliable.

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