Try sanding them up and treat with some Silkens oil. If the securing bolts aren't leaking then I would get a plug for the hole - they come in packs from whitworths.

If you want to take the whole thing off then a Sixaflex would be the go for re-seating them again.

The timber looks OK to me- would look great once sanded and oiled. Dont varnish unless you like sanding them back each season. Oil is easier as you just wipe them down with a rag that has some of the oil on it now and then.

If you are so inclined make up a canvas cover with press studs - keep the sun off and they will look great for ages.