Mercedes Benz 190E 2.6 transmission noise.
 

I have a 1990 190E 2.6 automatic trans and it has two problems, I hope I can get some advice from the members of this forum.

1- The transmission makes a hollow noise when shifting from 1st gear to 2nd gear only. The only way the car doesn't make the noise is when I step on the gas very gentle for a slow acceleration. What can I do to solve this problem? Is it a DIY thing or is it a major thing that only a mechanic can solve?

2- The Oil light comes up on the dashboard almost every 3 to 4 weeks, so I have to add oil to the engine. A couple of weeks ago I took it to a mechanic shop to have it checked and they told me that the main rear seal needed to be replaced. My question to you guys is, How bad is this leak? For how long can I keep adding oil to the engine without having a major problem?

Any suggestions would help. Thanks.