1999 e36 M3 evo roof problem

[Mikestrevs]

Greetings all, I'm new to the forum. I have just purchased a 1999 m3 evo convertible. I viewed the car and it has been raining in Cornwall for a few days and the owner said the hood hasn't been used for a few days because of the rain. Fair enough I thought. I operated the hood and it seemed fine went up and down fine. So I tried again and as it was going down it stuck and the owner just pulled the rear bar by the rear window and it was fine it went down. Same happened on the way back up he just pulled the rear bar by the window slightly and it worked fine. He said it could be the rear bar needs greasing but I wonder what it actually is and whether it is actually gonna cost a fortune. It only happens probably twice in about 10 attempts. Apart from that it's fine. I was wondering if anybody had any ideas please. Oh and by the way. What an amazing car it's so powerful and it just pulls and pulls in every gear. Awesome machine