The Feilun TT009 RC boat is a very popular 5 4 0 class RC boat well known for its low price and reasonable performance. However, due to cost reason it uses a PCB kind of integrated receiver and ESC unit which will eventually die after going through about 50 packs of 2S.
Instead of buying an original replacement, you can actually use the receiver box to hold a regular ESC. The boat itself is pretty water tight so I don’t really worry about the issue of water proofing. If the receiver box is not big enough for both the ESC and the receiver, you can 3 d print a small receiver mount and hold the receiver somewhere else. You may use hot glue to seal around the connections just in case water does accidentally leak in.
Once you replace these electronics, you will likely need to also replace the servo. The stock servo takes a power input that is receiver specific and may not work with your replacement unit.