That is $70 / window! If anything, tell them that you will get it repaired yourself. Lenders will not allow a seller to give repair funds to a buyer anyhow. One tube of caulk is about $4. You may have about $150 worth of caulk needed.
If your home is stucco, it is even more important that the caulking is maintained.
But, it is all part of the negotiation process. How bad do you want to sell, vs. how bad the buyer wants the home. only you can answer that.

Do you mean calk/sealing or do you mean you have double pane windows that are leaking between the glass - a broken seal? Not sure the second one can be remedied without a sash replacement.

If it's not an immediate safety hazard, I'd tell their agent that I understand that they are perhaps novice buyers and unfamiliar with handling on-going maintenance.

Then I'd offer to handle it for them before closing, if they pay labor and materials, but the price is not going to drop over a few tubes of caulk.

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My inspection report came back with a long list of items , most of which were boilerplate "maintenance issues to watch for" and only three were actual problems.