poppy

My Stags Horn tree (Rhus typhina) is about 30 years or so old and quite gnarled, a few patches of 'resin' and splits on the bark. It is quite large and until this year has had masses of leaves and fruits. It has the usual number of fruits but the leaves are very few and not large. It seems to be sending out slightly more suckers than usual. Has it come to the end of its lifespan or could it be diseased? The leaves are already turning red in some cases, 2 months too soon. Could I rejuvenate it by cutting back or would that make things worse? The only other difference here this year is that it has been raining non stop the whole of June and July and it was a wet winter whereas two years previously there have been bans on water hose use due to dry winters and summers - I know they dislike water logged soil, although the drainage is good. If it is an overwater problem would that suggest it will be ok next year if left (and the weather returns to normal). Many thanks for any help or suggestions. poppyx