Warning lamp issue.

Hello,
I have a new mfs 5 cs, i used it about 20h and break in time was successfully.
I have a problem and that happened 2 times. After i use the outboard half- between full throttle some time (10 minutes maybe), then i turn throttle to iddle and warning lamp starts to blinks few times in second.
Warning lamp is blinking only in iddle and %10-20 throttle. I doesn't blink over %20 throttle.
Warning lamp is not blinking after i stop the engine, tilt up, wait about 5 minutes and start up again.
I have a new, right engine oil and right level. Does anyone have any idea what is that mean?

You may have a flaky sender. You are in warranty, so ask your dealer to check the oil pressure with a mechanical gauge. If it's OK, replace the sender.
You should run 10w-30 non synthetic oil, and it needs to be between the hash marks on the stick.

Thank you for answer. I will contact with my dealer.
I use PRO Star Super Premium 4 Stroke 10W30 Outboard Oil - Synthetic Blend, is it wrong oil? It says it is fine for Nissan outboards.

I wanna ask 1 more thing, when i changed lower unit oil i used different kind of oil plug gasket. Orjiinal gasket was 15 mm(outside), 8 mm(inside), 1 mm thickness. What i did use red fiber gasket's inside and thickness was same but outside was 14mm so outside 1 mm smaller than original. Do you think does it cost any problem?

You should be fine.