It looks familiar but I can't place the brand.

If it has an aluminium body I would be ditching it and replacing it with a Henderson. All plastic with stainless bolts and pins and made at Cowes on the Isle Of Wight. About $190 for a complete pump and $90 for a recondition kit.

Don't recognise it from the pic, but it would be easy to replace the handle - any SS or thick-wall aluminium tubing of the right diameter will do.

To replace the diaphragm, no option but to remove it and extract the current diaphragm. You may find the name of the pump, and may even be lucky to find a compatible diaphragm if you visit a few chandleries with the old one in your pocket.

Can I borrow him for some jobs on my boat?

Took a few photos of mine, which is original and looks identical to what you have. It's a tmc-71601 diaphragm handpump. I was able to partially get in and take a photo of the base of the pump which had tmc on it, from there google did the rest. I managed to get a whole new pump via eBay for $66. That's the easy part. Not going to be easy to change. Luckily I only have a 32 waist.

http://tmcin.com/tmc-71601diaphragmhandpump.aspx

Its interesting that if you have a boat in survey in NSW 12volt pumps don't count! Only engine driven or manual pumps.