check out www.fgoc.co.uk for info on mk1 & mk2 Galaxy's.
They do make great tow cars, and I've never heard any reports of h/gasket failures. Maybe on the older mk1's with the 2lt petrol engine, but the 2.3 is great lump if a little thirsty (almost as much as the 2.8 v6!).
Max tow on mk1's is 1500kg (kerbweight around 1650 kg)
Max tow on mk2's is 2000kg (kerbweight around 1700 kg)
Be warned though, auto boxes on the galaxy, alhambra & sharan are well known and very costly weak points on the mk 1 & 2's (1k + for a recon box + fitting!).
Diesel's are more costly to buy, but have more torque and better fuel econemy.
I tow a 1050kg van with a 1999 mk1 TDI 90 bhp, and have never had any probs towing what so ever.