Replace head gasket at 225.000 miles?

[Guitarman]

Hi, I love my OUTBACK 2.5 liter 2003, but it has 225.000 miles (363.000 km). It runs on LPG. timing belt replaces last year. It is starting to leak a little water at the head gasket (to the outside). My mechanic says this is common for the 2.5 engine. Is it worth getting it repaired? are there any other engine failures to be expected?

Thank you