To be honest there are several service pubs out there. Each has it's strengths and weaknesses. The main one with the most info is from AGCO who owns Massey Ferguson. You can acquire all three pubs from them. I have found the users manual near my year on eBay which details basic maintenance. The service manual that most owners here have from AGCO can be purchased online www.agcopubs.com The I&T manual is like a thin magazine in size and covers areas Agco doesn't. Then there is the Jensales service manual I really can't comment on because I've not read one. If you have an eBay account I've seen these pubs go dirt cheap. I own the Agco service and parts book and a copy of the I&T manual. I scored the owners manual last year on eBay.
If you need to look up a part you can go to www.agcopartsbook.com and sign in as GUEST put in brand and type and pull up each section of the 135. However you must be using Microsoft Internet Explorer with Silverlight installed. Silverlight is MS windows version of a PDF viewer. A very helpful online tool. Good luck -kid