BMW Repair: bmw 3 series, oil light and consumption, cylinder head gasket, bmw 3 series

Question
2002 model, full serv history, not thrashed, cared for bmw, since last service and return to garage for seal swap as fitted incorrectly oil light repeatedly comes on and after cup of oil top up goes off only to come back 3-4 wks later for same. garage suggests cylinder head gasket or piston rings? advice would be appreciated, could wrong oil have been used as suggested on other sites? or leak in to cooling system perhaps another idea? no apparent leaks to be seen since seal changed.no smoke.otherwise beautiful car,average miles etc, but worrying, please help any advice appreciated.
thanks
Kev

Answer
How many miles are driven in two -three weeks and how many are on the car?Newer models do use a thinner grade oil and some only synthetic.If it has many miles I would try a thicker viscosity than you are using now.Any seals leaking will cause oil consumption leaking out as well as burning slightly.Rings or a head gasket could be determined by a compression test and a cylinder leak down test