MUNICH, Germany - It was in the late northern summer of 1972 that BMW announced "a new class", codenamed E12, that was to pave the way into the premium segment for the Bavarian automaker and the beginning of one of the most successful of business sedans.In 2012 BMW is celebrating 40 years of its 5 Series. Officially the 5 Series was unveiled at the Frankfurt auto show in 1972 featuring a 520 model with a 85kW engine and a 520i with 96kW. See the picture galleryBMW's design chief at the time, Paul Brag, gave the 5-Series clearly defined lines with a sporty character to compete against the more conservative and mundane cars in the segment such as the Mercedes W 114 and W115 as well as the Audi 100.A CLASSIC E12 FOR A BEER?Untill present day the typical BMW kidney grille and dual-headlights have been a design hallmark. From the start the automaker linked the sporty temperament with the requirements of a premium company car.In 1973 the first six cylinder BMW 525 was launched with an output of 107kW. In 1975 the 528 followed with a 2.8-litre 121kW power unit. That was still not enough as the German automaker's motorsport section pushed the envelope even further.The motorsport section tweaked it into an M535i with a whopping 160kW - the predecessor to the M5 that made its debut in 1985. At the time the weaker diesel engines played virtually no role in the vehicle's history. Today the 5-Series diesel engines make up three-quarters of the vehicles sold in Germany.Until the first generation change in 1981 BMW sold almost 700000 units. Meanwhile the 5-Series has entered the sixth generation with a production volume totalling seven million units.Meanwhile the first of the E12 series have become a rarity. Ulrich Thieme, who runs the www.E12.de website, believes there are only about 1500 of the first 5-Series cars still on the road in Germany.Thieme said: "The times when an old E12 could be bought for a case of beer are finally over." The M535i and 528i are especially sought after by collectors and easily cost about 10,000 euros, according to the expert.A drive in a 528 from the BMW Classic car collection in Munich takes you back to a time without the electronic aid of current vehicles. The car takes you gently through the curves and then develops a dangerous will of its own for any driver who has become too accustomed to an Electronic Stability Programme (ESP). It is a feeling many a BMW fan is yearning for.