Keith,
I have used the 33TTL for many years - Isotta are still very much in business (they have a website) but have been found to be very slow for servicing and repairs - one of the Reasons Ocean Optics gave up the dealership and the reason I stopped sending my guns to them.
I have sent my guns in the past to Equipesub (in Milan I think) for repair - they are an authorised Isotta service centre and have always done an excellent and quick job for me - my last was a battery replacement, which included an upgrade to higher capacity cells. I would send you their e-mail address, but unfortunately I am away from home working in Angola - back home around 15 Feb if you can wait until then. Please send me a personal mail to remind me.
As Paul says, these guns have a very nice soft light (reminds me of the old Subatec S100"s) - if you find them heavy buy a 1/4" cork mat, cut to size, steam it to soften and curve to the contour of the gun and slip it under the neoprene cover - you have a neutrally buoyant gun.
Hope that helps.
Regards,
Mark Webster
www.photec.co.uk