Sealant would be a get you home measure at best if it is the hg .
The days of engine rebuilds are long gone , unless , you are a mechanic , or have money to burn .
An engine swap would be the cheapest way out , unless you find another usable car cheap , but why would it be that cheap ? , another one with hg gone or about too ?
Engine from scrappie or ebay £250-500 , engine swap £100-200 , if you know a man who can ?
If not , scrap it for parts on ebay yourself , and put the money towards another black hole , oops , i meant car .
There is no easy cheap fix ,eng rebuild = £££££-
eng swap = ££-
scrap it = £££+
buy another = ££££-
best outcome = £-
good luck anyway .