The seller-side partner wants to change the split because the timeline slipped and he says he did more work during the extension

Whoever did more work during the extension has a fair grievance but zero legal ground without a clause.

What I want to know: did either of them sign anything acknowledging the extension, even just an email thread?

The title attorney's framing is precise, and it names the actual fault line. The split was not a fixed number; it was a proxy for expected work distribution. When the distribution changed, the agreement had nothing to say, so both partners retreated to the interpretation that favored them. That is not a dispute about fairness; it is a drafting gap.

The assumption doing the most work here is that deal complexity stays constant from signing to close. It almost never does. Lien clearance, buyer retention calls, extended negotiation with a title company, these are foreseeable events, and a well-drafted JV agreement treats them as such. The mechanism is a pre-agreed adjustment clause: if the closing date extends beyond X days for reasons attributable to seller-side work, the split moves by Y points; if it extends for reasons attributable to buyer-side work, it moves the other way; if it extends for reasons outside either party's control (a title defect is a plausible example), the original split holds and any incremental costs get reimbursed separately from the fee, not carved out of the other partner's share.

The risk neither partner named here is that the fee itself is now in jeopardy. A buyer who has been getting cold feet for three weeks, while two partners argue about who gets how much of a number they have not yet received, is a buyer who may walk. The split negotiation is consuming attention that belongs on deal retention. Confirm with a real estate attorney in your state on the enforceability of mid-deal renegotiation; some states have specific rules on assignment fee agreements that affect what either party can actually demand.

For any agreement going forward, the clause to add is explicit: what triggers a split adjustment, who decides whether a delay is attributable to which side, and whether costs incurred during an extension get treated as reimbursable line items or absorbed into the existing percentages.

What does the original agreement say about dispute resolution if the two partners cannot agree on a modification?