I am not the best pax to advise on maintaining the boots, because mine pairs arent in the best shape too. Best to bring your pair to the Orchard Gate Way shop for the staff's advice. I believe their standard recommendation will be three: Cleaner, Conditioner, and Protector. Clean liao, but leather will be dry, so will need to condition. Wash and condition liao, it has lose the layer of protection, so will need spray the later of Protector...
I am too lazy for so many steps. So basically I am only using cleaner, then rub on mink-oil. Since my pairs already "cui" kind of beyond cure liao... haha
I think best is still bring back to Orchard Gate Way shop bah seek their advice bah. Previously they will recommend to go shukey at far east, but that had pretty bad feedbacks too. Recent years I heard they do take inhouse request for resoles.
TBH, I don't see any local cobbler or shoe repairs has the right tools and expertise to fix them properly...
I heard OGL folks has collab with a Taiwanese who does very good resoling service.