This is from a letter to the Chairs and Ranking Members of the Senate Finance Committee and House Social Security Subcommittee from the Social Security Advisory Board (SSAB) (footnote omitted):
In light of efforts to reduce the federal real property footprint, the Social Security Advisory Board (Board) writes to highlight a unique issue for the Social Security Administration (SSA) regarding property acquired with money from the Social Security trust funds.
The Board believes that any proceeds from the sale of trust fund acquired property should go to the trust funds. Trust fund dollars are for Social Security program purposes only and have been intentionally set apart from general revenues by Congress. The Board therefore encourages Congress to direct all revenue from the disposition of trust fund properties to the trust funds.
By the way, I think that SSAB has closed its doors but I haven’t seen proof that it’s happened.