Found Unknown Damage After Signing Lease Transfer Addendum. Can That Null The "as-is" Clause If It Was Not Disclosed?

Location: PA USA

I am the current tenant of a unit. My landlord would not let me terminate my lease (even paying it out) and forced me to find a new tenant. I did. The new tenant walked through the apartment and I showed them the very small damages I knew of. They signed the lease transfer addendum saying they were taking over the lease and all responsibilities of the unit. In the email explaining the transfer, it was stated multiple times the unit was taken of "as-is". The signed transfer says "current condition". Not sure if that matters. In a kind gesture, I also gave them my entire 1300 deposit without requesting any reimbursement (before I even knew about the damage). It was transferred by the management company automatically but the management company recommended I ask for reimbursement.

Now I am cleaning out the unit and I found a stain in the hardwood that was under a rug. I had no idea it was there. I can't estimate the cost truly. It may be under the 1300 deposit. It may not be.

Could the new tenant argue I lied about the condition and break the agreement? I am 100% willing to contact the new tenant and in good faith agree to pay anything above the 1300 upon their move out but I am worried about putting that in writing in case it causes other issues. I just cannot have this lease transfer fall through somehow. It's not about the damage. I accept responsibility for that and wish they got a whole new lease and I could deal with this separately.

What should I do?