I'll add my $0.02
I had a 2001 E46 325Ci, loved that car to pieces. It was a money pit though. I purchased cash in 2006 with around 32k miles on the odometer. Drove it until I had about 69k, from 2006 through 2010, just over 4 years or so, before I sold it for just over half of what I paid.
I averaged out the cost of the car, minus what I sold it for, plus all the maintenance and repairs - even with a 3rd party warranty which I did have and in my experience is not anything close to a factory warranty - and realized I could have been leasing a brand new 3 series for the same money in that time period. Although I did customize the hell out of that car.
Therefore I understand your reason for wanting to sell. Those that are saying to keep it, you need to calculate true cost of ownership against the cost of financing a newer car. I would say, in fact, rather than finance a used 135i thats out of warranty or close to it, look into leasing a new 135i instead. Make mods that can be un-modded and sold later. Also there is no rule that says you can't sell a leased car - I did this with my X6.
As for your income and expenses and parents helping - that's all your business. From a purely financial perspective, it makes more sense to lease or buy (if you plan to keep longer than 6 years or so and like to mod your cars) new than deal with out of warranty repairs on a German car. If it was a Toyota, it would be a different story. That's been my experience.
I leased an X6 after I sold my 325Ci due to family needs - had a wife and a kid, so an SLK and an E46 325Ci weren't really cutting it anymore
Honestly, now I just lease all of my cars and don't worry about maintenance, ever. Always under warranty, free BMW service - in the case of Benz I prepay the service or roll it into the lease, so it's the same thing - I never worry about my cars anymore. Now I have 2 kids and a business, so for me not worrying about my cars has become more important than personalizing them.