to my personal experience keeping the filter in engine bay is a bit easy to keep an eye on.. plus it takes less hassle to change it when needed (all the filters are designed to be installed inside the engine bay, they can bear the heat, so keeping them there wont be a problem unless u place it correctly i.e BEFORE the fuel pump not in between fuel pump and carburetor thats a BIG risk..) dont fill the gearbox REPLACE all the gear oil, u need 2.5 litres of SAE 90 grade gear oil to do the complete job, u shouldnt use PSO oils, get hands on a high end brand FUCHS brand is quite common for bugs here, plus u should get hands on a good quality neoprene rubber axle boots, they'll surely last much much longer