Low compression in cylinder 1 on 240D

[airfoill]

Hello to the group. I've been having a rough idle problem/starting problem on my 240D that started in June. Starting was getting more and more difficult but ran fine after start. The car does use oil which is about a quart every 600 miles.

Then one day all of a sudden the engine started running as though on only 3 cylinders and had a very rough idle. I did a compression test and all cylinders were around 300-340 except cylinder number 1 which was 100 which explained why it ran so rough. So I did the simple test to see if it was either the valves or the rings so I poured about 1 tablespoon of oil into the glow plug hole and did a retest of the compression.....similar result....about 110. I decided it was the valves because the compression never came up appreciably.

Last month I pulled the head off and sent it off to the machine shop that specialises in head rebuilding. The head came back professionally rebuilt with brand new exhaust valves and a brand new gasket kit with new head gasket. Installed the head and attempted a start. I got the same result. It was very hard to start but eventually got it stated and ran rough at idle just like before but seemed to run a little better. I did another compression test and the results came out the same with number 1 cylinder at 100. I poured some oil into number 1 cylinder and retested the compression I still have the same low compression. I always though that if it was the rings, the compression would shoot way up with the oil poured into the cylinder......this never happened during the compression test. What am I doing wrong? I am so discouraged by this after spending all the time and money taking the head off and getting it rebuilt just to have the same results. I know it isn't the head so it's got to be the rings but can the rings be so bad that the oil can't make a temporary seal for the test? I've read Marvel Mystery Oil but does that really help? What do you guys think?

Thanks

Herb