Bumpy

Beginner on this site, so I hope this query ends up in the correct forum! On my 3rd Forester, love them! However, they have a hard life with me! I tow a trailer (1.5tonne+) for my male voice choir. Already burned out a clutch. Ouch! Manoeuvring in car park on full lock reverse, I've damaged the diff or a u/j. Every time I use full lock now it sounds as if a cog is 'popping' Any ideas what I should encourage the garage to check? No doubt an expensive repair. Any advice (and sympathy) welcome!