mazda bongo advice please

having now pinned down our needs to something like a mazda bongo - i know that they are called "grey vans" that we will have no idea of history before importing to England. seen one at a garage converted really nicely by denby conversions. bit cramped for my husband and i with a side conversion but think will be fine if we just use for weekends etc. the guy selling took it in part exchange and has only its last mot certificate and no history but it had only one owner since it came to the uk in 2009. i looked underneath and there was a bit of oil on the "square thing" under the van so i put my hand on it and it came away with oil. my husband asked the guy and he said its the gearbox and that there is always going to be a bit of oil around that area. is that true? it has aobut 67,000 miles (is in km on the clock) since registered in the uk. test drive seemed fine. we are unsure of what it is like to get serviced in the uk and what parts are like to get. it seems good value at £7995 and the guy said he would do a service and new mot and new cam belt. but am worried about the oil thing. any advice or any others out there who have had bongos  i would love your experience. we will be using it for my son to sleep in the top. wondering if it gets too hot in the summer? thanks