Never, ever use Rad Seal or other sealants. Yes, it may block up a leak, which is good, but some of the waterways around the engine can be very small bore and the sealant also does a good job of sealing those too, which is very bad.
You need to do things like this on level ground, doing it on a slope is only going to give you headaches.
I think there's also a drain plug on the engine block somewhere but can't look at the workshop manual for you until later this afternoon.