Hello...I have a LGB starter kit with w/51 inch round brass track using engine 20212 Stainz. I use it around my Christmas tree. This past year, I noticed the engine was not maintaining speed. It would slow down and speed up sporadically. I am trying to figure out if it may be due to the power pack or engine motor. I took a multimeter to the power track and it measured approx. 25 V DC at the wire connectors. I then hooked up wires to track and tested the rails at each section, which consistently measured at the same approx. 25 V DC. I cleaned rails/track and made sure wheels and shoes of train were clean. I put engine on tracks and continued to notice engine speed up and slow down with no change in speed control. I took the multimeter to track to check V DC under load and noticed fluctuations that directly correlated to the train speeding up and down. It appears to be happening randomly. Is this enough to go on to determine whether or not I need to replace my power pack? The train lights continue to function correctly...it is hard to tell if they dim but the speed variance is noticeable. I have the original power pack...LGB 50081, which is rated at input 120V AC 60Hz and output 0-24V DC 20VA. Any suggestions and advice would be appreciated. Thank you!