Hi Miguel,
i dont know a lot but i hope this helps.
the M specification after 36 M Mk 1 stands for Mesapotamia and means that the gren was specially waterproofed for a tropical climate to prevent blinds or duds. This was originally introduced with the no 23 M Mk 11 and went on with the No 23 M Mk111 and the 36 M Mk1. Normal grens were also produced at this time. My documents date from Jan 1918.
The grens were marked slightly differently, standard versions had the top of the gren painted red, M examples had a line of 3 red crosses along the side of the top 3 segments with a half inc filler band around the centre.
The waterproofing consisted of chinese wax or madagascar beeswax 20 parts, unvulcanised rubber 2 parts lanoline 78 parts and the gren was prepared as follows;
The spring, striker,and pivots of striker lever are to be lightly coated with oil or mineral jelly[vaseline i suppose]. Before inserting the centre piece in the grenade the threads are to be coated with waterproofing composition.In order to make the joint between the top of the centre piece and the grenade airtight the same composition may be used or alternatively a mixture of methylated spirit and shellac.With either of these mixtures or without them if desired a lead washer may be used with the centre piece screwed well home on the washer.A fillet of the waterproofing compisition is to be placed round the edge of the striker hole in the top of the grenade and also workedinto the groove round the striker.
The joints between the centrepiece and the grenade body are to be made absolutly airtight. The threads of the base plug are to be coated with an anti-corrosive grease.
As i said before normal unwaterproofed grens were also made at the same time and this whole process started during WW1, although by WW2, all 36s were so treated and all marked No 36 M Mk1. I think it was common sense in the end do do this to all the grens, even though it increased both production costs and the time it took to make the gren.
Hope this helps,
Andy