Another thing you need to consider is tires, i have seen people putting the car on jack stand. It can not leave the car for 2 years on a good set of tires, they will develop flat spot.

 

The best option is to do the storage procedure outlined above, and then simply don't be lazy about driving your own car when you're back here for 2-3 weeks. Problem solved.

If you don't think you can manage to move your mom's to get yours out when you're back here every few months - then yes, sell it.

 

Don't sell her if you love her,invest in a battery tender system and do drive the car when you get home.

 

Don't sell it, give it to me to look after for you. I promise I will try not to drive it too fast or very far.

 

+1 if you're planning to keep it follow the storage procedure outlined, I'm in the same situation (minus the coming back bit) and I sold given the following:
1) Depreciation will mean 2 years down the road I could buy a younger e60 with the cash from the sale, at about the same mileage if not less and poss higher spec.
2) Battery tenders are good but, you will need to fully service the car in situ if it doesnt move for two years (Cost and it will be a bit of pain to sort)
3) Tyres will also age... it's been mentioned about flat spots and keeping the weight off the tyres, but rubber will also age.
4) Rubber pipes / electrical connections will also age, so you will need to do a full inspection once your back

For me, It came down to cost vs effort in keeping it, the maths dont stack up for me, but if you love the car I can see why you want to keep it

I already miss mine and every time I see an E60 in the same colour I catch myself checking the plate to see if its mine

Good luck what ever you decide

 

The other big potential issue with letting a car sit that long without running or driving it is that gaskets and seals normally under pressure and lubricated can dry out/shrink which will result in leaks and potentially significant repair bills. Sell it or make sure you start/drive it periodically.

 

sell it.

 

Use tender battery charger then have your mom starts your car every 2 weeks or 4 weeks for 15'min then stop. that will keep the gasket lubricate prevent from dry out and cracks and don't have to move the car.
+1 Sell it .. get another one when you get back from 2 yrs. You have mentioned that you come back every 3-4 months for 2 weeks but not using your car so what the point to keep it ?

 

She should move the car, to move the tires around (as somebody else already pointed out).

But the bigger question, is why did we dig up a 4 month old thread? The OP has probably long ago made his decision.

 

Yeah I agree with others. Tires would be a big concern sitting and developing flat spots. Crap my Conti's do this just sitting overnight. What about the tranny? I've known three people who had non bmw's and allowed the car to sit for an extended period of time and then they all had transmission problems. I heard that portions of the belts or something in there can become dry as the fluids are all sitting in the Bolton instead of moving. Not sure if this would even be an issue with BMW. But if you are coming back every 3-4 month I would just drive it a few miles.