Sealant on T1-11 siding

This is a condition that I find myself writing up all the time on new construction. Applying sealant at top of trim board that covers horizontal joints between T1-11 siding. The seller of this house has asked the builder to install the sealant that was called out in my report. The seller claims that by installing the sealant will void the manufacturers warranty. Can some of you other inspectors give some insight into this subject that I can share with the buyer? Thank you in advance for your help.

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