Removable motor HOBs can leak. AquaClear has replacement O-Rings available for that reason.

I've been using canister filters off and on for several decades. Seals occasionally leak due to physical issues. Other than that leaks are user caused. The cure for most user issues is a thin film of silicone grease or petroleum jelly on the seal. Most seals are silicone so petroleum jelly or grease is safe to use.