Not familiar with this machine, but googling reveals a pic or 2 to give me some ideas.
Open steam valve and pump some pressure backwards up the steam line. I have made a fitting from a car tyre valve and a bit of tubing. I connect to a bike pump with a gauge. Pump it up in stages to 20psi (1.5bar ish), check for leaks as pressure raises. You can even shut steam valve and check it holds pressure over time or look for leaks with bubbly water. You can then increase pressure some more to check safety valve operation. You will need to check what pressure it should vent at.
So you can now find/fix leaks in the boiler circuit with a cold machine.
Then plug it in and let it heat up knowing that it is ok. Check brew path with pressure gauge, check pump free flow figures.
Fat and grease is easy to remove with caustic. Try looking at labels on bbq cleaner and oven cleaner. Careful it will eat aluminium.