We are a small servicer and are exempt from providing monthly periodic statements. If we do provide a summary of monthly mortgage payment transactions as a courtesy to a borrower, does the summary need to meet the 1026.41(d) content rules?

No. You're exempt from 1026.41. It might be a best practice (especially if you plan to lose small servicer status or ever want to sub service anything), but you can send them whatever you want as long as it doesn't run afoul of anything else (UDAAP, state laws, etc.)