Welcome! There are a couple of good UK groups on Facebook, more active than here (which to be fair is more US based). The Mercedes 320 engine is strong and not known for gasket failures. I’d get an independent Mercedes specialist to look first. Yes on the battery, get a new one, so many unreleased gremlins stem from it. Car looks tidy, and yellow is quite a rare colour. Have fun on the recommission, and enjoy the drive.